Please HELP! I really need advice!

I've been with my boyfriend for a little over a year. When we first started dating, we had sex quite often and it slowed down to maybe once a week. The last few months, it's been twice a month if I'm lucky. Every time I come on to him he doesn't want to do it. He says "it's not happening tonight." It makes me feel crazy unwanted, unattractive and hurt. 
He masturbates a lot. With porn. I used to have a huge problem with that, but I've begun working on accepting it since we talked about it. We usually have really good communication with things. However, when I talk to him about needing more from him sexually, he just blows me off. He'll say that I'm too sexual, we are always busy (we definitely are NOT), he's tired whenever I ask him, and that sometimes he just doesn't want to do it (he should say all the time). We got into a really big fight the other night and he got pissed saying that this shouldn't be such a big deal. But it is to me. 
I don't feel like I should always have to initiate sex, especially since he'll say no anyway. But if I wait for him, we're having sex less and less often and I feel like it will never happen. He calls me selfish and that I should accept when he doesn't want to have sex. I feel like he's the selfish one always masturbating and never coming to me when he gets the urge! 
Ive tried explaining to him that I need this emotionally, it's not just physical for me. I can't make him understand. What should I do?!