Should i cut off my bestfriend? (kinda long)?

so my best friend (who is a girl) is great. the thing is im in love with her.... which sucks because i know she doesn't feel that way about me. It hurts me whenever she goes out with someone else, and recently she has started fooling around with one of my guy best friends (which she asked me and i stupidly told her it was ok) its just the friendship hurts too much because i hate seeing her with other guys and i love her. Im not going to tell her because it would make it akward, but what i think im going to do is if she goes into a relationship with my friend, ill probably just text her and tell her everything, and tell her that the friendship hurts too much to continue, and please dont talk to me anymore (not out of anger but out of sadness) what do you guys think?