Hey, thanks for the understanding, Anneintherain (love that name!). She would like the two of us guys to be friends and allies and that is the biggest reason she would rather I didn't leave when he visits.
My partner who's also on this forum as Mara reminded me that she had broken up with her other guy as she and I were coming together but then reinitiated with him when we decided to open up the relationship. I realized on a long run last night that I had envisioned courting a mutual partner with the new open relationship. Her bringing back her ex and my checking out my own ex's has brought some distance to our partnership, though we are talking about it now and committed to finding a way to be loving and supportive of each other. I didn't realize how much writing it down and receiving the perspective of others more experienced in multiple partner relationships would help clarify some confusing and contradictory feelings so thanks to the forum and all those who've responded so far.