Why won't he sleep with me?

My boyfriend and I have been together for almost 2 years and he won't sleep with me. It's not that we don't want to, because I definitely do and he keeps saying he does and he never can keep his hands off me but when it comes down to it or if we ever get full alone time where we can, he just doesn't go through with it. I don't wanna push him and I've told him if he's not ready or not comfortable told let me know and he always says "I want to have sex with you, it's not that". I don't know what to do or how to make him want me I guess? I'm 19 and he's 18, we've had sex maybe once and it was only for a few minutes before we just stopped. I've talked to him about it numerous times but I'm just all out of options and I don't wanna be a bitch about it :/