Have you actually tried talking to him, in a kind, non-sarcastic or angry way? Can you put your needs aside long enough to possibly think that perhaps his lack of intimacy with you, has more to do with the relationship, than just the act of sex?

Pressure to perform includes asking. It also includes pouting and acting like an immature 18 year old, which I suspect you do in my opinion. He goes to work in the morning and knows that the problem with the lack of sex is going to be there when he gets home. That is pressure. He knows that you are unhappy with him, that is also pressure. He knows that you are unsatisfied, that is also pressure. Declining your sexual advances is also pressure. Your expectations pressure him whether words are spoken or not.

It is terrible to be sexually rejected without an obvious reason. I do agree with you, but perhaps you are going about this the wrong way.

Try, as has been said, to talk to him. Just try to listen to what's going on with him without jumping to conclusions he's got someone on the side. You could suggest the two of you go to counselling. Perhaps he needs to have a physical exam with his Doctor to see if there are any underlying problems that could be causing this.

This is only one problem out of a million that could cause a rift in a relationship. It could be the relationship itself- who knows. But, if you react this strongly that it is all about you, instead of concentrating on him, and trying to find solutions, you won't get anywhere.