I miss him...

My boyfriend and I haven't had sex in a little over two weeks. It's not that he's not horny- the first thing he does when he comes home is masturbate. And I'm definitely down for it, but when I approach him he tells me that he's tired or not in the mood. For my birthday last week all I wanted was dinner, scary movies and maybe a little make-out session. I got an argument and me sleeping on the couch instead. In the morning I'm leaving for a week and he decided to spend my last night here with his guy friends drinking and playing Dungeons and Dragons. Why doesn't he look at me like I'm sexy anymore? Why doesn't he want to have sex with me? What did I do wrong?