I caught my sister's boyfriend cheating on her, tell her about it?

Since you already was against the relationship from day 1 and she knows that.She is just going to think that this is another way for you to try to break them up. Even though you are her brother and she should trust you. got to think both ways. The best thing to do is let her find out for herself.I was in a horrible relationship and my sister was telling me that he is no good for me and I was so in love that I just stood by him.I had to realize it for myself to get out of that relationship.
- A way to do it anonymously is to try to set him up.So she can see.

yea tell her dude.

Tell your sister the truth in a loving way, with no intentions of your own. Just be prepared for her to either not believe you or not do anything about it. Don't be surprised or angry at her if they break up and then she takes him back. You have done the loving thing by telling her, then step back and let her handle it however she wants to. She is the one in this relationship, and it is her decision how she handles it. Just let her know that you love her and wanted her to know the truth.

It's going to hurt her no matter how she finds out. You might as well tell her now instead of waiting for her to catch him in the act--who knows how long that could take? Say she doesn't find out for a month. For that month, she'll still be with him while you know the truth. I think that would hurt her too.

Yes I would tell her. She might be mad at you at first but later she will thank you for it, when she finds out from others and knows it's true!

been a while since I've had to deal with this stuff but umm what id do is tell her but let her down slowly and gently if she needs to be left alone then you respect that cause you sound like you respect your sister a lot so you know tell her slowly and gently.

if you saw him then you should tell her about him instead of waiting .

See here's the problem: if she's that into him she won't believe a word you say, so what you do or don't do doesn't matter. I only say this because I was in this same situation with my sister once.

I would tell her, if you don't you're denying her information that she'd clearly use to make a different decision. She shouldn't have to spend more time in the dark with a guy who could really be a cheater.

She needs the information so she can ask him about it personally.