You certainly know what the score is. Continue to share with him all of the experiences you've had by communicating on this forum. Encourage him to check out this site and some of the links that have been provided by posters on this site. He needs a dose of reality and the sooner the better. I think part of the problem may be that right now he thinks he has her where he wants her, since they're obviously communicating and spending time together at the moment. It's hard to convince someone that they're headed down the wrong path when things are going their way. Problem is, eventually the novelty will wear off for her, just like it did last time, then she'll be cheating on him all over again. Maybe that's when he'll wake up and smell the coffee but it'd be much better for him to beat her to the punch. I'm not suggesting that he should just go out and sleep with someone else for spite but he needs to back off, be aloof, not return calls/messages right away, hang out with his other female friends, the whole nine yards ; you know the drill. Just keep trying to convince him but don't be too disappointed if he doesn't respond positively. Remember, you can lead them to the water but you can't make them drink.