And sometimes the love isn't there to mend things. I guess it depends a lot upon the type of affair - a drunken grope is easier to forgive than repeating indiscriminations over a period of time.
Sorry m8, but my advice is born of experience and that's all I can talk about. All the love in the world cannot change anyone if they don't truly love you back and I've learned the (idiot's) hard way that some people don't really commit their hearts to relationships sometimes.
As to whether he should try again, I guess it depends if he feels that there is something still alive in the relationship that can make it work. If he does, then why not? (but lay some ground rules out like not again, and if it is again - DO NOT involve the daughter AT ALL). If he doesn't, then it won't work anyway.