The problem is this

What if I'm starting to have real feelings for J?

I was always crushing on him. I never would have gone to his dance class by myself (being as I'm shy in social situations) but I met him the week before and he had seen me around at my job. He made me so nervous those first few weeks. He'd dance with me and I'd immediately mess up. I didn't expect the attraction to take hold quite as fiercely as it did. But now I find myself not happy when he hasn't called me or when I haven't run into him, and there is the whole raging jealousy of last week.

I saw some program a long time ago about how thee chemical released in a woman's brain during an orgasm make her start having warm, fuzzy, romantic thoughts about the guy she's just slept with. Which makes it harder for women to have just sexual encounters and is why many women have that whole "wake up in love" moment the next morning (maybe not literally the next morning). I so wanted to be able to "just have fun" with J and not get hung up on the fact that he seems to just want the sex and no strings, no dates.