Friends(backstabbers)

Can anyone in mibba land help me with something here's the problem OK: so me and my 'best friend" and my crush are hanging out in my living room and they went to my room while i went to the bathroom room and played Sims2 for a couple min. thinking they were just talking so Wednesday came along and other of my Friend's came and pulled me aside and told me something about my 2 friends and turns out they made out well here's the problem she knew i liked him, it just pisses me off To end that she would do something like that to me so i really need some advise