That's an important point, not to be missed. If he has a need for external validation, particularly in the form of romantic attention from women (this was my ex-husband to the letter) then this is a problem that is not going to go away unless he recognizes it, and does the long, hard work to deal with it. In my ex's case, he never did. So we would go through these periods of "remission", where he would not be engaged in intrigue with other women, but eventually he'd relapse. (I'm deliberately using the language of addiction btw, because that's what it was.)

I went through this cycle sooooo many times. And in the end the only way to break the cycle was to be out of that relationship.