"A Problem Page For All!"

Just be a good friend and stand by her with whatever she decides. At 17, maybe she feels mature enough to be in a relationship with the older guy and so long as there's no violence or inappropriate behaviour going on between the two of them, then it has to be their choice to stay together and if you force her to give him up, she'll resent you for it and it could harm your friendship...

Boyfriends come and go, but friends will be there through the good times and the bad; stick by her and try to cheer her up when she's feeling down and if things go wrong, help her pick up the pieces...

I think that's all i can say i'm afraid. good luck!