Sex, long term relationship.

Okay, I've been with my bf over a year. I moved in afew months ago. Back recently say 6 months we had sex a lot. But over the last few months he barely wants to do it. When we do its good. I n that th he seems to enjoy it when we do. But it's so infrequent its almost like hes losing interest. As I said earlier we used to do it a lot. He's the only person I've ever slept with.... is it me or is this normal in a relationship? We have also had some rough patches lately. But everything seems okay on that score for the most part.