The sex

I realized something today that I guess I never really thought of before. I realized that when it comes to sex, I'm much more interested in convincing the girl to sleep with me, then I am in the act itself. It's like I seduce a woman and it's great. Then say we start dating and it's a month down the road, I start to lose interest. Not in the girl necessarily, but in having sex with her. Is this normal? This is how it has always been with me, so it makes me wonder. I think it has to do with the whole idealization and devaluation concept that is so common in borderlines. The woman is way up there because she is not giving in to going to bed with me. Once that happens, down she goes..she is trash in my eyes. Nothing to be proud of, just reality.