(( VaginaPagina ))

My housemate went thru something really similar. It turned out for her at least, that his sex drive was just much lower then hers- after the initial couply stage, it just dropped off drastically. It happens, it sucks, but it happens. Talking about it helps, she also found that there are random little things that sometimes help too (if he just has a low sex drive). One is putting a dab of your own juices (ok, that sounds nasty just typing it, but i couldnt think of another word), on your neck. Something about pheramones (sp), is like a little fuck me signal. She says everytime she does it, he jumps her. I think everyone in the house has tried it and for some reason it works.
Definately talk to him about it though, you deserve to know why its just not happening.