First off don't destroy yourself. I mean if you think it's all behind you and them then forgive and realize these thing happen in life. But if you feel your mate is likely to repeat this behaviour then get out. I've seen this sort of thing happen several times. We are humans with sex at the root of our being. Sometimes you meet someone and as the chemistry heats up over time you just do it. Then you are locked into a bond. And don't think it can't happen to you. Under the right circumstances it can. So project love into the situation and patience and understanding. He has to grow up and value his marriage. Maybe by now he has. An affair like you describe will always cause mental damage leading to alcoholism or depression and last for some time after the affair is over. It's on the subconscious level and can't be talked away. It's partly because of a great mental conflict that says 'I want to be with my new lover all the time but I can't because of my home life."

Then again divorce may be right because of the threat when your daughter visits. You will always see her but just at a place away from your ex. Then go on and enjoy life while realizing these thing happen and don't drag it around with you endlessly. Don't discuss it with friends.