Long distance relationships and sex?

Ok well my boyfriend and I have been together for 3.5 years. We did live together but I had to move temporarily an hour away due to a job intern at the Mayo Clinic, being that we aren't going to be moving here, and he has a very good job where we used to live, we just see each other every weekend. When we lived together our sex life was fantastic sometimes 3-4 times a day.

He drives down to see me every weekend and he's a good boyfriend takes me out places, brings me dinner flowers, alcohol and seems like he'd do anything for me and says I don't Sometimes I feel he comes down here expecting sex? I mean of course cuz yeah I'm his gf I understand..but sometimes we do it throughout the weekend, but there are sometimes I'm just not in the mood, even for the whole weekend and I'm not sure why? And he gets upset and says "you don't see me for a whole week why aren't you in the mood?" I mean is it bad I don't want to do it EVERY weekend he comes? Is that wrong of me? Even if I just do it one time during the weekend..he wants it the next day and the next day and if I'm not in the mood he thinks I'm not as interested in him as I used to be..and that's not the cast at all. I just don't understand, if I am not in the mood why does he have to get mad every time? He's so nice and respectful with everything else. I understand to some of you I may come of as selfish but im really not...when we have sex we are both equally pleased. Is it weird I want a sex free weekend sometimes??