Would you tell your friend that their partner is cheating on them?

Absolutely. In the end, I would want to know. But do it as gently as you can. And when your friend gets angry at you and says you don't know what you're saying or what you are talking about....let your friend know you don't blame your friend for being angry it's a hard thing to deal with and when that friend is ready to talk or whatever you will be there. When it comes down to it, it's your friends decision to either believe you and take action or not believe you and turn a blind eye. The best thing you can do is be the support your friend needs whenever your friend needs it period.

No. I've been in this exact position before. I would definitely speak to the one who was cheating, but not to the cheatee.

If I was 100 percent certain and if I had proof. Absolutely!

My first thought is no. But, it would depend on the situation. And I would try to figure out a way to help them figure it out themselves.

Nope never again, I told him that and it was like it was all my damn fault, So nope let them find out for themselves.

I did once and will never again. I lost my freind over this, she did not believe me or another mutual friend. We knew the girl he was cheating with even saw them out together several times.

been there done that never again

I wouldn't. You'll probably lose two friends: The cheater will be pissed that you ratted them out, the other will be resentful that you knew.

You have to make sure that you know for certain that this person is cheating.
If it was me, I'd Either tell my friend. And if he/she didn't believe me i'd be like o.k fine. but i'll be waiting to say i told you so. Then i guess i'd just be there for my friend if and when she gets hurt.
OR
thee's always the option of catching him/her out yourself. Film it. tell you friend first. if she doesn't believe you. then show her the video. It might be harsh and hurful. But it would be better than my friend falling in love etc. then finding out what a scum bag her partner is and get hurt even more.

i'd lead them too it probably(like fungirlmmm said), but honestly i dont know from personal experience...

Yes!!!
They are gonna get hurt by you for saying that, but they will be hurt more by their partner later.

No....I'd just remind them I was there for them if they needed me. It's not my business to break up a love.

NO!
stay out of it!
You'll loose both friends.
It happened to me. i know.

Not if you want to keep them as a friend....For I promise you this...If you do...then it will be you that gets dropped....

Better to drop hints....and hope for the best.....But if they ask...the yes....do it

I am in this situation right now. I know for a fact he is cheating on her, but I don't have the guts to tell her... she loves him so much. I just can't do it.

It depends on the circumstances (how close of a friend, how sure I was about the cheating, how serious of a relationship they were in), but I probably would not tell. It's really none of my business (maybe she already knows and doesn't care, maybe they're in an open relationship, maybe she is cheating too, who knows!?) I'd make sure my friend knew I was there for him or her, but I would stay out of it otherwise.

Nothing like watching your friend on the Jerry Springer show.

i have been in this position before. i told my friend that her bf was sleeping with my room mate and she chose to shoot the messenger, so to speak. she gave up our friendship and we didn't speak for 14 years but not once did i regret my decision to tell her. i figured her giving up our friendship was her loss, not mine. her bf was no gem and she knew it. he was pretty much cheating on her from day one and she was aware of it.