Don't say a damn thing. Trust me. This stuff blows up. No matter what you say, and how true it is, she will say your just jealous and trying to break them up. Sometimes you just need to move on. It sucks ass, I have a problem where I have to move on cause I am at school now, so far from home. You should still try to be friends with them, atleast her. If I remember correctly, you're not that old. The relationship won't last through HS, so stay friends with her cause ya never know where that will lead.