I have this.. acquaintance who is the most terrible person when it comes to relationships. She never listens to her friends, she constantly complains about problems she herself creates with her boyfriends, and she is one of the biggest hypocrites I've ever seen.
Recently I went out with her and a few of my friends, and she brought along her new boyfriend. He's a really nice guy, and we became friends. I thought about warning him about how she is about...well everyone, but before I could do that, she created drama out of nothing(i heard the conversation)and pissed him off something awful, causing the relationship to end.
A few months later I see on facebook that she's talking to him, wanting to make up. Now he's the dilemma. Does persuading him to be careful, and cautioning him about her relationship tendencies mean I'm doing something good more than bad, or am I just putting my nose in where it doesn't belong by letting him get in to a shipwreak again?

i would say , if he has not learned his lesson after all these , it would be better to leave them alone , being a matter of personal choice , it might be that he finds something in her , that makes him attuned to her . anther thing is you would not save him every time he makes a mistake , so it is better to let him get the experience . he would be more cautious after wards .

Agree with Firefly

Another thing is also our thoughts.

If he later start to wish that he had tried out the reunion, and his mind find out how well this had gone, and how wonderful life then would have been (daydreams), then there was only one guilty person who had prevented this nice Image to come through.......YOU

We all live our life....We are all Unique....We all think different.....a good friend gives support, and advices if asked, if we try to control others life to fit  our owns opinions, then we are nothing more then a puppet master trying to clone other to be ourself.

He knows what he walk into....and I think let him have his experience

i do not agree with firefly. agree that he has not learnt from his experiences. but i do not agree with the point that he should not be saved or warned this time. see, it is not much about the person. it is about a mistake. if you see any any one just about to commit a mistake, isn't it your duty to warn him/her? would you let a blind person fall into the open manhole, just because you saved him last time when he was going to stumble onto the drain. not done, dear.

facevalue, warn your friend this time also. there's no harm helping the same person again and again.

Help a person again and again till he awakes... I think Confused Mind shared the right word at the right time....