Freud wrote: "Where they love they do not desire and where they desire they cannot love." Whatever your feelings about this statement, it sounds as if it might resonate with you. Despite all your efforts and wishes, you cannot get desire going in your head. You feel so sad about it, because you have not consciously changed, it is more likely your unconscious that has changed and is responding by powering down, causing upset, and then switching off. I can only wonder about the causes for this. Three years is a long-term relationship, and the sexual connection may well be much more emotional than physical at this point. You live together; I don't know your age, are there plans for a baby? What are your intentions towards each other? Are there things to say that cannot be said between you? How do you negotiate the things between you in your otherwise "perfect" relationship? How much has the "in love" look been damaged by your "dread" of spending time with your boyfriend who can also "pester" and "repulse" you? Can you talk about this together? Can you ask yourself some questions about being "turned on"? You will have lots of history to draw on about what made you feel "sexy" in the past.