I did a tag search for divorce, because I am in a similar (not same) situation. A year before we introduced poly, our sex life took a turn. I think it might be just me, but whatever it is, I can't finish having sex with him when I start. I feel used. I try to just stick it out for him, but essential "rape" myself by being physically not into it as I allow him to take more. I would be sore the next day, complete with bleeding from the trauma I allowed to be inflicted. He is not a bad guy, and most of the time he thought I was into it. That was my own communication error. I have talked to him about it 3 times since then. Our sex life has dropped off because every time I think of him that way, I think of pain.
So this last time we had sex, I did it again, after not doing that for months. It was the worse that it has ever been. I realized why I feel like I am being raped, its because he is just taking, he isn't interested in giving pleasure. We've been married for 7 years now, he KNOWS what I like, yet he does nothing to please me. That is why I feel used. So after this time I have been actually scared of sex with him. It was something I completely brushed aside until I told one of my poly ex's (whom I am good friends with) and he made me promise not to put myself in that situation again. It made me realize that there are some real problems here that shouldn't be ignored.
Right then. So now I hardly spend time at home, he and I are more like friends/roommates and I don't plan on having sex with him again. I have told him all of this, and said "I feel selfish for keeping you in a marriage that isn't completely satisfying". He really really doesn't want to split (which is good, I guess), but I don't think he realizes the gravity of the situation. I don't love him like I used to. I don't think all is lost yet, but I am leaning that way. I am searching the net for other's in similar situations. I don't want to split our family up, but I want to make choices that will be best for everyone. I am wondering about separation. I am wondering if he could just accept that we are roommates, a new relationship status, and give me a little more freedom in that.
Good luck with your situation, please feel free to PM me for support.
Have courage to continue this journey, for it holds nothing but lessons and wonders.