I wonder how different things would have been if you'd come from a place of self-respect compassion rather than going in for the angry accusatory drama?
You: H, I've learned that you are still in frequent contact with your BFF. That really isn't OK with me. It has to stop.
H: It's perfectly innocent, we're just friends.
You: She is not a friend to us, not a friend to our M. Anyone who is not a friend to our M should not be in our lives. I'm not OK with it. I won't live with it.
H: It isn't that easy, she was there when I needed someone and you weren't. She cares about me.
You: I'm so sorry I wan't there then. I am now. I can see it must be hard and painful to let go of someone who was so important to you, who felt saw you and cared. I can see how it would be hard for her too. You've both made emotional investments and it hurts to end things. I'm so sorry you both have painful feelings to deal with. But, it still needs to end. Continuing the R will only bring more pain. It isn't fair to either of you to continue it and it is not good for our M or me. It isn't good for anyone. Painful as it is, it must stop. I must respect myself and our M here. I need you to write an open letter to her that I mail, or to have a final phone call to which I can listed. So long, goodbye, it is over. We were there at an important time in each others' lives, but that R is not part of my future. I need to say goodbye firmly and to put my romantic R and partnership with my W first. I will block your cell number and email address, please do not try to contact me otherwise."
H: I don't know if I can do that or want to do that.
You: I understand, it is a hard choice. For me, the R has to end completely for me to want to be part of the happy, passionate, vibrant M I think we can have. I'm not interested in anything less. I'm open for trying for that with you now if there are only us in our M and all our friends are friends to the M. But, I'm also a big girl and need to take care of myself. To me, that means not staying in an M while you continue your relationship with BFF. It doesn't work for me. That is something I am very clear on.
H: I don't know what you expect me to do.
You: That is really up to you. I've let you know where I am. It is time to be done with that R. A firm goodbye and then no more contact. But that is of course your choice to make, and I understand it is a hard and painful choice no matter what happens. It is really OK to try with me and change your mind later. That won't make you a bad guy. But for me, right now, it is not OK to continue to be with you while she's still involved. It's just not what I'm looking for in my life no matter how much I love you.