You should communicate with him, not us. That's the first thing. Online forums are a guide, but not a substitute, for solving your own relationship issues.
Secondly, you should ask if there's something bothering him. Maybe he likes you but is worried he can't be a good father if you get preg (assuming this is straight sex). Maybe he sees porn, and the reality is not what the porn advertises, or the fantasy is getting in the way of real sex somehow. Maybe he's unsure about new positions. Maybe he's not confident about his prowess, or worried that he's boring because he only likes two positions.
The thing is, you can't find any of that out by talking to us. You gotta talk to HIM.