Well, it sounds like you want to do the mature thing and let go of a relationship with someone who has unavoidable toxicity surrounding him - even though it will break your heart to do so. Is there any way you can continue your relationship with him and just not be around her or interact with her? There's no requirement in poly to endure the presence of toxic metamours - it certainly isn't unreasonable to ask that he can see you outside his home and your contact with her can be very little to none.
But if that isn't possible and a breakup is inevitable, then I would simply ask to talk to him privately and then express to him some of the things you wrote in your posts:
"Honey, you know I am deeply in love with you, and when we are together, it's euphoric. We're so well-matched in so many ways, and we have an amazing time together. We compliment each other, challenge each other, and I haven't felt so strongly about someone in a very long time.
But I am struggling with the dynamic of this Vee. My heart is breaking to tell you this, but I don't feel I have a lot of other choices. The drama of your other relationship, and how you allow it to continue, along with the challenge of our schedules, is just very unhealthy for me. The drama has just been too much for me, and is very difficult for me to deal with. It's not working for me, and I know it's not likely to change.
I don't want to end it, really, because I love you, but the reality is - I need to end it. I know you want to marry me but, given the rest of the situation, it's not a solution I think is workable long-term. I don't want to cause you pain, but I feel the only thing I can do in order to be in a healthy place in my life is to let go of this toxic situation."
Last edited by nycindie; 09-26-2013 at 01:52 AM.