Loss of interest?

I have been dating my boyfriend now for four years. We have known each other since pre school. In the first year or so in the relationship he couldnt seem to get enough of sex with me. Use to have to stop after a while because it began to hurt.

Now it seems that he is no longer interested. I have caught porn on his computer a few times but he doesnt usually go on it. But lately any time I try to get his attention he just doesnt even bother looking. He likes to just sit on his computer and play his video games. And talk to his friends on there. He never has been very social outside of the computer either with our friends.

Ill try to flash him and he doesnt even bother to look up from the computer screen. Ill walk into the room naked same reaction. Maybe once every two months or so we will have sex. But usually when im in the mood if he does pay attention to anything it will start off with me giving him oral. During which he barley touches me at all and after word he goes right back to being on the computer.

When we do have sex it just seems to end quickly. Not like ten minuts quickly but it seems like he just wants to get it over with most of the time. There are very few occasions where he seems to enjoy it anymore. when I have asked him about this he sometimes doesnt comment and other times he will say thats stupid.

Is it me? Is something wrong with me? And how do i get him to tell me whats going on without him getting defsive or make this into a arguement...?