Ok some will flame for prior circumstance so up front idc what your opinion is so why share it?

Anyway she met someone at work and has feels for him and we discussed how to deal with it. I was towards co-dating because they were new and I don't want to keep her from exploring, she is young yet. Idk really know how we got there but since he's not poly she figured he'd leave. We had talked about poly but I had issues the first encounter and asked we not be as I worked on myself and we worked on our relationship. Obviously that boundary didn't exist to her. Now we are broken up and supposed to be best friends. For me this is difficult because I still have all the emotions for her and I see the same in her often even though I know she is hiding it. Just days before this we were talking of moving in and now that is gone. I feel betrayed but I also see she was scared and also scared of hurting me. She is bipolar and adhd and I think a lot of this is that.

I'm leaning towards sticking it out and being her best friend and just seeing what happens. Two reasons she is my best friend and I want to be in view when this crashes because she can be a bad partner and he doesn't seem the most stable.

Idk I'd like constructive thoughts but the negativity about moral issues you can leave at the door.