Yeah, but that's the easy part. The whole time I've always tried to do as recommended, investigate and determine what the oher person offers to your spouse that you didn't. Actually no it's not. It's EASY to pick up books etc...that tell you what might have been the problem or LEAD you into thinking you know what some of the problems were - those things are great and they are extremely helpful. But there ain't nothing like that school of hard knocks. Where you learn what you've learned because YOU are living it and IT DAWNED ON YOU, with no outside help. Do not ever discount that. It's in the valleys of your life that you will grow the most.
Unfortunately there's only 2 things I can come up with and one of which is verifiable: he 'parties' with her all night (verifable) and provides a better sex life. Well...I'll put it to you like this: parties don't last forever. And neither do d*cks. Of ANY kind. So know that sooner or later, it's gonna come time to pay the piper. And the landlord and the electric bill, the cable bill, etc... and all his "shine" is gonna start to look very dull. Because he is not a man of substance. Not one like you, that though flawed, is here trying to save your family. So to hell with your image of the other guy. Don't get caught up in the same delusion your wife is in where he's concerned. Keep it real.
