2 cents: A man married and divorced four times knows how to appear to be what each particular woman happens to want, but doesn't know how to be in a true authentic romantic partnership.
Red flag, yeah, I'd say. But only if you are looking for marriage material. Dating, maybe ok, unless, of course, you are feeling vulnerable and needy, looking for someone who will appear to be exactly who you want...
Contrarily, I think Mitch's life may go just fine. I think the kids may very well adapt and continue to love him. He may live happily every after with LP and thrive professionally.
SO WHAT?
You ask why his life is going well? Because he is bringing things into it that he finds hugely important and fulfilling, even if it is scary and requires change and risk. He is perhaps a bit too focused on himself right now, but he will swing back into a more moderate mode most likely. When we change or lives, we often go to an extreme before we gentle back to a better mean.
What are you bringing into your life that you have longed for, perhaps even forgotten you wanted?
Your life will be better with him out of it than it was with him in it. Why is it a problem if the same is true of him? Please tell me you aren't still holding onto being right, lol. It is really OK for you both to have wonderful lives.