Whats wrong with me CAN YOU HELP ME?

Okay so my boyfriends bestfriend who is my bestfriend is about to hook up with a girl my boyfriend and i know wont be good for him cuz our bestfriend breaks girls hearts. we wont try to stop him but my problem is that. I think about our bestfriend and this girl (i use to like this guy and i still kinda do) and well i throw up literally when i think about him or her. idk whats wrong with me but this hasnt happened before. HELP!!!!!!!!!!1