user-1: What is sex without attachment to sense pleasure actually like? Does it feel different? Do you only ever have sex to please the other person? I'm asking both about the relationship and the act itself.
Clearly, you don't need celibacy to achieve jhana (some zen monks have wives). What is being renounced if we continue to engage in sexual relationships? Would engagement in sex with oneself (only) be proof that one cannot obtain the jhanas? etc..


For achieving these absorptions, the overcoming of the five
hindrances [including sensual desire], at least temporarily, is a preliminary condition. It is
especially in the context of achieving the absorptions that the Buddha
often mentions the five hindrances in his discourses.


user471: For monks and nuns, the full time professional practitioners seeking complete liberation from suffering, the advice given for food, craving and conceit is that relying on these, liberation is pursued, but these are to be abandoned upon complete liberation from suffering.
But sex is not relied upon and it's to be abandoned completely in the pursuit of complete liberation from suffering, by monks and nuns.
The Pali suttas have no notion of tantric sex or sex used in a way that leads to enlightenment. In other words, there is no sex without clinging to sensual pleasure, unlike food.

Then Ven. Ananda approached the nun and, on arrival, sat down on a
prepared seat. As he was sitting there, he said to the nun: “This
body, sister, comes into being through food. And yet it is by relying
on food that food is to be abandoned.
“This body comes into being through craving. And yet it is by relying
on craving that craving is to be abandoned.
“This body comes into being through conceit. And yet it is by relying
on conceit that conceit is to be abandoned.
“This body comes into being through sexual intercourse. Sexual
intercourse is to be abandoned. With regard to sexual intercourse, the
Buddha declares the cutting off of the bridge.
AN 4.159


user24057: 
What is sex without attachment to sense pleasure actually like?

The sensory experience of sex or masturbation is at its root merely a physical experience. It is a body phenomenon common to humans with bodies. Sexual pleasure and sensations can be used as an object of meditation, not unlike the breath or a candle flame. Most people become absorbed in this merging with the meditation object and may lose awareness that this is all only consciousness and modifications of consciousness. For most humans, there is an arising of grasping when orgasm approaches. This can be transcended with practice, and the orgasm may be experienced as "no big deal."

Does it feel different?

I would say yes. Once the dissipative orgasms are transcended through yogic practice, regenerative orgasms become possible. These can be very different in body location, intensity, duration, and spacious involvement of others, than what most humans experience through common dissipative orgasms (those that once you have one, your desire to continue sex is diminished)

Do you only ever have sex to please the other person?

The deeper question is, what serves and liberates love and consciousness? What terms and conditions have you agreed to with your significant other in this area of sex? There are many factors, and in general, I would say "no" to only having sex to please others; however, if you are in a tantric consort relationship, you may, for the sake of growth and experimentation, trust your partner's guidance in this area sometimes more than your own discrimination and personal preferences.

What is being renounced if we continue to engage in sexual relationships?

You are renouncing any hope of sex ever fulfilling your ego, solving dukkha, or changing your basic nature.

Would engagement in sex with oneself (only) be proof that one cannot obtain the jhanas? etc..

No. It is a natural body function. It produces state experiences that may be attractive but do not resolve the existential pain of this realm.

user16635: I think you might want to reflect on what sex with attachments is like. Think of the kinds of attachments that commonly result from sexual activity:

There's greed or hunger, a craving for more, greater, different experiences of pleasure
There's pride and jealousy, the desire to declare one's conquests or to have what another has already declared
There's fear — fear of inadequacy, fear of loss, fear of shame, fear of commitment — and fear binds us to fight or flight

The pleasurable aspects of sex is not (in and of itself) problematic. But sexual activity is one of the most karmic activities we can engage in, because it explicitly and implicitly creates changes in our relationship to world around us, with everyone having to adjust to the new conditions. And resistance to change is at the root of all dukkha and tanhā.
Sex in the absence of attachments — well, let's call it 'dharmic' sex, though that term will likely get with disapproval — is actually quite natural. I mean, it's easy to lose track of both your 'self' and your partner's 'self' in the heat of the moment, though it's extremely difficult to keep the egoic self from snapping back into place after the fact (that's the goal of Tantric practices, but one shouldn't adopt those incautiously). At that moment, it isn't about pleasing your partner or yourself, because both of your egoic selves have been set aside. It's merely an open experience of pleasure, in which your pleasure and your partner's are intertwined and indistinguishable. It's not too different from the bliss that arises during jhana, though obviously the latter is more calm and focused, and much easier to maintain. Pleasure is a mental, experience, a result of liberation from the egoic self; the physical pleasure of sex acts as a catalyst for that mental liberation, much as the physical stillness of meditation acts as a catalyst.
If you want to achieve that catalytic effect through sex, you need to establish intimacy and trust with your partner. Intimacy and trust are functions of the egoic mind, yes, but they set the stage for that momentary release of egoic identity, we can't go into sex with fears, worries, and doubts and expect to be transported.

-1: <p>What is sex without attachment to sense pleasure actually like? Does it feel different? Do you only ever have sex to please the other person? I'm asking both about the relationship and the act itself.</p>
<p>Clearly, you don't need celibacy to achieve jhana (some zen monks have wives). What is being renounced if we continue to engage in sexual relationships? Would engagement in sex with oneself (only) be proof that one cannot obtain the jhanas? etc..</p>
<hr />
<blockquote>
<p>For achieving these absorptions, the overcoming of the five
hindrances [including sensual desire], at least temporarily, is a preliminary condition. It is
especially in the context of achieving the absorptions that the Buddha
often mentions the five hindrances in his discourses.</p>
</blockquote>
 471: <p>For monks and nuns, the full time professional practitioners seeking complete liberation from suffering, the advice given for food, craving and conceit is that relying on these, liberation is pursued, but these are to be abandoned upon complete liberation from suffering.</p>
<p>But sex is not relied upon and it's to be abandoned completely in the pursuit of complete liberation from suffering, by monks and nuns.</p>
<p>The Pali suttas have no notion of tantric sex or sex used in a way that leads to enlightenment. In other words, <strong>there is no sex without clinging to sensual pleasure, unlike <a href="https://www.accesstoinsight.org/tipitaka/sn/sn12/sn12.063.than.html" rel="nofollow noreferrer">food</a></strong>.</p>
<blockquote>
<p>Then Ven. Ananda approached the nun and, on arrival, sat down on a
prepared seat. As he was sitting there, he said to the nun: “This
body, sister, comes into being through food. And yet it is by relying
on food that food is to be abandoned.</p>
<p>“This body comes into being through craving. And yet it is by relying
on craving that craving is to be abandoned.</p>
<p>“This body comes into being through conceit. And yet it is by relying
on conceit that conceit is to be abandoned.</p>
<p>“This body comes into being through sexual intercourse. Sexual
intercourse is to be abandoned. <strong>With regard to sexual intercourse, the
Buddha declares the cutting off of the bridge.</strong></p>
<p><a href="https://suttacentral.net/an4.159/en/thanissaro" rel="nofollow noreferrer">AN 4.159</a></p>
</blockquote>
 24057: <blockquote>
<p>What is sex without attachment to sense pleasure actually like?</p>
</blockquote>
<p>The sensory experience of sex or masturbation is at its root merely a physical experience. It is a body phenomenon common to humans with bodies. Sexual pleasure and sensations can be used as an object of meditation, not unlike the breath or a candle flame. Most people become absorbed in this merging with the meditation object and may lose awareness that this is all only consciousness and modifications of consciousness. For most humans, there is an arising of grasping when orgasm approaches. This can be transcended with practice, and the orgasm may be experienced as &quot;no big deal.&quot;</p>
<blockquote>
<p>Does it feel different?</p>
</blockquote>
<p>I would say yes. Once the dissipative orgasms are transcended through yogic practice, regenerative orgasms become possible. These can be very different in body location, intensity, duration, and spacious involvement of others, than what most humans experience through common dissipative orgasms (those that once you have one, your desire to continue sex is diminished)</p>
<blockquote>
<p>Do you only ever have sex to please the other person?</p>
</blockquote>
<p>The deeper question is, what serves and liberates love and consciousness? What terms and conditions have you agreed to with your significant other in this area of sex? There are many factors, and in general, I would say &quot;no&quot; to only having sex to please others; however, if you are in a tantric consort relationship, you may, for the sake of growth and experimentation, trust your partner's guidance in this area sometimes more than your own discrimination and personal preferences.</p>
<blockquote>
<p>What is being renounced if we continue to engage in sexual relationships?</p>
</blockquote>
<p>You are renouncing any hope of sex ever fulfilling your ego, solving dukkha, or changing your basic nature.</p>
<blockquote>
<p>Would engagement in sex with oneself (only) be proof that one cannot obtain the jhanas? etc..</p>
</blockquote>
<p>No. It is a natural body function. It produces state experiences that may be attractive but do not resolve the existential pain of this realm.</p>
 16635: <p>I think you might want to reflect on what sex <em>with</em> attachments is like. Think of the kinds of attachments that commonly result from sexual activity:</p>
<ul>
<li>There's greed or hunger, a craving for more, greater, different experiences of pleasure</li>
<li>There's pride and jealousy, the desire to declare one's conquests or to have what another has already declared</li>
<li>There's fear — fear of inadequacy, fear of loss, fear of shame, fear of commitment — and fear binds us to fight or flight</li>
</ul>
<p>The pleasurable aspects of sex is not (in and of itself) problematic. But sexual activity is one of the most karmic activities we can engage in, because it explicitly and implicitly creates changes in our relationship to world around us, with everyone having to adjust to the new conditions. And resistance to change is at the root of all dukkha and tanhā.</p>
<p>Sex in the absence of attachments — well, let's call it 'dharmic' sex, though that term will likely get with disapproval — is actually quite natural. I mean, it's easy to lose track of both your 'self' and your partner's 'self' in the heat of the moment, though it's extremely difficult to keep the egoic self from snapping back into place after the fact (that's the goal of Tantric practices, but one shouldn't adopt those incautiously). At that moment, it isn't about pleasing your partner or yourself, because both of your egoic selves have been set aside. It's merely an open experience of pleasure, in which your pleasure and your partner's are intertwined and indistinguishable. It's not too different from the bliss that arises during jhana, though obviously the latter is more calm and focused, and much easier to maintain. Pleasure is a mental, experience, a result of liberation from the egoic self; the physical pleasure of sex acts as a catalyst for that mental liberation, much as the physical stillness of meditation acts as a catalyst.</p>
<p>If you want to achieve that catalytic effect through sex, you need to establish intimacy and trust with your partner. Intimacy and trust are functions of the egoic mind, yes, but they set the stage for that momentary release of egoic identity, we can't go into sex with fears, worries, and doubts and expect to be transported.</p>
