NEED ADVICE ASAP

Okay, so my friend Trisha has been talking to this boy Ian lately. I was always kinda weird about it, because she is so sweet and he is more experienced than her. I'm pretty protective over her because she is an angel. But my friend, Rose, told me that the other day her and Ian were studying together and left to study at Ian's house instead. Then one thing led to another and she gave him head. KNOWING THAT IAN IS TALKING TO TRISHA. It gets worse, after she told me this, Ian and Trisha both walked up holding hands... AND HE JUST ASKED HER TO HOMECOMING! Do I tell Trisha and ruin my relationship with Rose? Or is it just not my place?