Your previous post (sorry if I misread) that you can only have sex when you *intend* pregnancy is not accurate regarding Church teaching.  You don't have to intend it, just allow it.  I read your first comment, for example, to be saying that having sex with a woman who is naturally not able to conceive (e.g. after menopause) would be considered a sin.  It is not.  

The question of having sex in a way that "avoids pregnancy", which seems a new one in this thread, is definitely more complicated.  While the Church generally teaches that natural family planning is not sinful, it can be used in a way that the Church teaches is wrong.  

 The point is that we are not supposed to use people for gratification, even ourselves, even with consent. Love people, use things, not the other way around.