He doesnt want with me? have i done something wrong?

my boyfriend is 21 im 18 we have been together for 4 months now but im beginning to feel like ive done something wrong. he is currently away for a few months but came back for a week, obviously with not seeing him in a while i couldn't wait for us to be together. in my head i thought we would be at it like rabbits before he left again for another month. however in the whole week we had 3 times and 2 failed attempts (once he got hurt the other couldn't come) on many occasions i tried to seduce him but i failed miserably. i feel like he doesn't fancy me and when i confronted him about it he said he does fancy me and also said if the roles were reversed and he was chasing me for then he would come across as the bad guy. im not chasing him for , i just really am attracted to him and for me brings to people together. he said i clearly have a higher drive then he does and on days when we had already had and i tried to initiate it later on in the day his response was "no thanks im fine ive already had sexy today". when we do have sex he is in control and doesn't let me unless he is really tired. there's hardly any intimacy while doing the deed so to speak with very limited eye contact. he isn't a guy who comes out with his feelings, he doesn't tell me he loves me or anything like that, but i do know he cares for me with other actions outside of the bedroom. when it comes to having sex and not being able to come what exactly can be the cause of that? he said it was because he was tired and he had been up all night with no sleep at all, i just don't know of that can be the cause? i feel like im not being a good girlfriend but i just want advice and opinions of what might be going on. in fairness he did come back for exams and has been really stressed with university as he doesn't know if he will be allowed to return next year. anyone have any suggestions as to what might be going on here or something i can do in the future?