According to Mike Treder's list, IEET's 31st most popular posted item of 2010 was "Your Brain on Sexual Imagery" by Andrea Kuszewski. I don't have a lot to say about this one, but do have a look at it. It offers a nice potted discussion of the neurophysiology of sexual arousal and pleasure, exploring such things as the way we feel bonded with someone that we've just had sex with ... and how the effect can linger.
I'm not sure what the implications are, apart from the fact that it's good advice (mine not Kuszewski's) to avoid having sex with anyone you don't actually like. It's better not to go through life feeling emotionally bonded with somebody you find physically attractive but who is actually, at least in your perception, a nasty piece of work. Unfortunately, just fantasising sexually about somebody will also create some of that feeling of being emotionally bonded, especially if your fantasies lead to orgasm.
So watch out! Choose your fantasy objects carefully.