Hi, Phrick~

I think Rhiannosmoon is on the right track about the purpose of "marriage" theory.

To (try to) answer your question, (the title of OP), why do you feel so guilty regarding sex?
Perhaps it is because of how we are raised in this culture of ours that women, (especially the "wife role"), are expected to perform once we commit into a relationship. As though one of the marriage vows, sex is an expectation of provision. I'm really not sure.

I do know, though, that I simply do not have ANY interest, desire or even thoughts of sex with my husband. I used to feel guilty about it. I used to endlessly ride myself about it. I used to try to provide for him what he needed despite how I felt, but each time made me feel even worse about myself.
It has become so bad that I finally encouraged him to find outside means for satisfaction so long as he was safe about it and I was left alone. And he did, which I am perfectly fine with. (Please understand that I am in no way suggesting that that is an option for your situation. That is a last resort that doesn't work for everyone).

You and your husband still have the love for each other that can get you through these tough times. It's the love and commitment to each other that supports ANY relationship.

I wish you and your husband all the best.

Shangrala