Do I leave my cheating husband or share him with someone?

I've been with my husband for eight years now. We have split twice before, and the first time was because he cheated. I took him back months later, and he really tried making it up to me by making a lot of changes. However, we continued to have issues because of my lack of trust. My insecurities and trust issues lead to physical abuse, which lead to us separating again. During that separation, he consoled himself by talking to the same girl he cheated on me with. But we then ended up back together and worked it out for a while until I got pregnant with our second child. The baby was a few months old, and he confessed to me about his secret relationship with her. He told me how he could never stop talking to her and how, during our issues, she has been and is the only women he's gone behind my back with (but on a friendship level because she's miles away). He confessed how he fought feelings for her and feels like he's possibly in love with her too. He said he feels like he's in love with the both of us now because this women has fallen for him, and she hasn't been able to leave him alone since. Even though she knows that he's still with me and happy with our family, she can't help it, and he confessed how his feeling for her are mutual. Being that he loves me too, he wanted to be with the both of us at the same time. He wanted to have affairs with her behind my back by flying her out and staying at a hotels, but he didn't want me to find out, so he told me everything. He said he didn't want to continue to lie to me and so I can finally stop accusing him of being with other women when it's only been this one girl the whole time. He feels like my insecurities and trust issues are what pushed him closer towards her, and that no matter what he did to do right, I would still accuse him. He's caught up in his feelings and pretty much says that he wants her but doesn't want me to leave him because I'm the one he wants to be with for the rest of his life. I'm of course hurt and in shock. I feel like I have to make a decision on whether I want to allow it and deal with having to share him or walk away. Both of these decisions are really hard to make because I feel like whether I stay or go, my heart will still be torn apart. I have to make a decision quick because she will be flying out sooner than I thought.