What should I do, my sister has a friend, who she really like being with. But I don't know if she should be hanging out with him . . . normally she is super happy after talking to him, but today she was sad. I had never thought about him in any negative ways. But she made a promise, not to tell something to anyone. Now I have lied to her to try to help this guy. I also don't know if her friend or if she is in danger. What do I do?
I can't let her get hurt again because I didn't fix it!

I would personally tell your sister’s friend to either do whatever makes her happy but if you truely think their “relationship” or “friendship” will end badly.. give her good reasons to just end it before he does badly. Don’t lie to her though, probably the worst thing to do because once she does find out somehow you lied to her, you’re also putting your “friendship” in jeopardy. Since you already did, I would tell her the truth and tell her your side to things and your opinion but before you do, make sure she wants to hear it. If something takes a turn, be the mature person and make sure to not involve yourself in the situation to much because it can cause more drama and a bigger situation that’s most likely not called for. :)