I dont want to sound like your shrink but
Wife maybe but to the kids no way there's no point chasing a relationship with someone from 13 years ago just to be made to look like a tool the fact that you have even contemplated it would make you look like a sleeze to her. Feelings you felt why would it matter now
But he's unhappy with his wife and sticking around for the kids, which is fucking selfish by the way. Unfair to the wife (he will eventually cheat on her with the first bitch that gives him a little attention) and unfair to the kids (way to go, let's show them what a dysfunctional relationship looks like).
Marriage Isn't constant lovey dovey kisses and hot sex in the closet. Kids complicate things and both parties are probably slipping on the spousal duties. They need to stop dicking around and rediscover each other. And he, especially, needs to stop being a selfish prick and remember that there is a reason he married his wife in the first place.
Stop being a pussy. Either man up and be a faithful husband and father and be happy with what you have in life, or grow a fucking pair and tell your wife you are unhappy and need a change. There is no other choice.