Boyfriend admits to wanting friend

My boyfriend admitted he was attracted to my best friend and would want to be intimate with her what am I supposed to do I want them not to be friends anymore I regret introducing them and I feel so stupid now im wondering if I should break up with him or not.

(More info below)

Update: I've asked him if he wants an open relationship and he says he honestly doesn't know but he knows he wants me for sure and he'll talk to me later. I've told my best friend this and she's upset with him as well. I'm insecure about being brown skinned having short hair and about my thighs I know im beautiful but I dont feel that way sometimes with the beauty standards where I live. And my best friend is the opposite she's pale with long hair and blue eyes and she's very thin. I just can't believe he said that we had a great relationship for it all to throw away but I guess it was never real anyway. It feels like I'm going to die my heart hurts so much.

(Also posted on other forums)

Advice needed