Simply: Girlfriend cheated with BFF, wants V to have us both...

[ablexi]

Is allowing a poly- permissive cheating in such a case? I feel as if it is rewarding her betrayal of my trust in our monogamous relationship.

I'm long distance, havn't met her yet, but we've been together 4 months. He's her BFF, dated once in the past, felt it awkward like "brother & sister" and now they slept together and she's uncertain as to our future, but would like me to share her with her BFF.

I'm unsure what to do, because how am I to trust her in the future. I know Poly's(Since I've been reading a lot) are involving trust like any other relationship, and betraying that trust is just as bad as is in a mono-.

Edit: The options seem to be break up with her, or allow her to continue the relationship.