should i tell my friend if her boyfriend is cheating on her?...

You must tell her the truth. She is your friend and you will never want your friend to be cheated

Thats a hard situation... It could go 2 different ways. 1.) she wont believe you and possibly get mad and say you are just jealous of what they have, 2.) she will find out from someone else and get mad at you because you didn't say anything. The best thing to do is tell her. If she gets mad then you need to explain to her what you have seen at the club. Mention that he saw you and he even said hi to you. Even if you have to be sneaky about it. Try getting him to the club and tell him that your friend wont be with you because she is busy or whatever. If your phone has a recording option or video on it, try getting him in the act. That way, you got proof and then you can be completely honest with your friend. Its sneaky and bad towards him, but its your friend we are trying to help out... Either way you decide how to go about it, she really needs to know. You don't want her to think everything is okay when its not. She doesnt deserve that, and its only going to be harder on you and her if you wait to tell her. Good luck hope this helps.

i guess your friend will feel bad if you will tell her about it thinking that you might just trying to ruin their relationship since you know she love him. so i guess its better to bring your friend with you so she will see her bf with another girl out of her very own eyes. then she will decide if she want to broke up with him or not, at least you showed her the proof about his bf.

you should tell her that her bf is dating someone else. think if she would find out that by herself and then he would tell that you knew it all the time. just be honest to her i would like to know if my girlfriend would cheat on me even if i would found out that from some of my friend.