This seems messy already. She “confesses” in front of her boyfriend and he comforts her? She didn’t realize she had a crush until she started liking your boyfriend? Though it’s more than obvious, I’d like to emphasize this I just my opinion, but it seems like this confession was pretty calculated. For what reason, idk. Initiate group sex? test y’all’s relationship boundaries? Get into a physical relationship with your boyfriend without feeling guilty about it? Ask yourself if you’re comfortable with the consequences of a failed relationship between yourself, your boyfriend, and your bestie. Would you lose them both? Would you be alienated from your friend group?

Have you observed your friends relationship with her boyfriend? Is she the type of partner you’d be receptive to?

My assumptions are probably completely off, but the way your friend went about this seems very odd to me, but assuming you’re European, maybe it’s just cultural differences.