I am in a very similar situation, only a bit more evolved on the poly end. My husband and I rarely have sex. We both have great drive and we used to have awesome chemistry together, but for the last two years its been gone. I just don't want to have sex with my husband anymore. I have a boyfriend who more than sates my sexual thirst, and that is alright.
I hear "relationship broken, don't add more" all too often, but in my experience, every relationship has issues to fix, all the time. Some times are tougher than others. Also, you haven't had sex in way wayy too long, I would consider you getting that fulfillment paramount to your current relationship, as it might help relieve some pressure and help you focus on issues.
I often wonder if my husband and I should split. We don't fight or anything, we love each other. But it is more of a familial love at this point. I care for him as the father of my children and a good friend, but that is about it. In dating a new man I have realized just how much I have been going without for years now. He cares for me and is actively attracted to me. It is just something that I need to be happy, to feel sexually attractive to another person. You have these rights too.
Please PM me if you want someone to talk to in great detail about any issues you are having.
Have courage to continue this journey, for it holds nothing but lessons and wonders.