Awww, c'mon, calling people names isnt going to get anyone anywhere...
and anyhow, you cant help who you fall in love with.
HOWEVER, you can help what you do about it.
I think she should back off and not mess around with a married man with kids, if he decides to leave the wife and take up a new relationship then go for it, divorcees are people too.
He should not mess around, it hurts everyone. If he is not happy with his marrage he should leave then he can shag the crack of dawn till the cows come home.
Morpheus, you should stay out of it, especially if you have romantic feelings for the girl, the only way to get involved without creating a big mess would be to send photos to the guy and the girl anonimously (like LazyKevin suggested), that way they can realise that people know about it, and then perhaps they will make the right choice.