The issue seems to be there's no emotional connection in when it comes to sex, and no emotional intimacy. (And it's important to note that porn usually lacks such things in a glaring way. This isn't an accident) 

It seems clear from your post that you haven't the faintest clue what your boyfriend is really feeling underneath. 

This isn't necessarily your fault, and I suspect he's refusing to talk to you about his sexual feelings, completely shutting down and stonewalling you. This would be because 1) he doesn't know how to articulate them because: denial, 2) he's terrified of being vulnerable in that way with you.

So, in this way the lack of sex is probably just a side effect of the breakdown of deeper intimacy in your relationship.

Perhaps not so surprisingly, men have emotional needs when it comes to sex that are just as strong as women's. But  it's often the case that men absorb the idea that you're not supposed to talk about it, the reasons for this are often complex. 

Most men do not enjoy sex with someone they don't trust, don't feel emotionally connected to and feel  doesn't understand their needs, any more than you would enjoy it. 

But again he may not understand why he feels uncomfortable, nervous and frustrated, this isn't your fault because he's not really talking. He's making excuses.