If she's not capable, or willing, then a choice has to be made. Till death to us part is not automatic. Sorry. Each party is entitled to happiness and fulfillment. If somebody becomes an alcoholic, drug user, felon, batterer is it until death? Of course not. What about if they become verbally abusive and won't change? I wouldn't stay. How about if they become a hoarder? I can't live like that, so after umpteen attempts at counseling I'd be gone. If they stop caring for themselves physically or deny intimacy I'm gone too. Of course after multiple attempts at therapy. You married her, she deserves a shot.
I will say that after my wife saw that 70% of my friends are now divorced she tries even harder to make our marriage great. Doesn't take me for granted, and hasn't turned down an initiation for sex in 5 years. Also doing Cardio Barre religiously. Smart woman - she knows what we have is great and wants it to continue. By the way, all of the guys (40's and 50's) who now have fractured families and twenty something's they are sleeping with said they would switch places with me tomorrow. But I was lucky or smart in choosing a great life partner, and it's better now than it was when we married 28 years ago. But we've always been best friends too. Don't think we've ever had a real fight.
But if my wife even refused to acknowledge an issue, and made zero attempt even if it was important to me, it would be rough to stay. I would think she thinks the same way. You get what you put into all relationships. And if your wife isn't putting in she just might not have a relationship to worry about anymore.
Can you unpack this a little bit? You're saying they're hooking up with much younger women, but still aren't happy? What do they miss about being married, their wife, kids full-time? Did they initiate the divorce? Just curious since for folks our age in unhappy marriages, I'd think hooking up with some young strange would be great.
1) The financial hit is ROUGH. All are struggling. At one point 2 divorced guys were living with the 3rd divorce guy. One couch surfs 3 nights a week at my friend's house and then spends a few nights a week at her apartment, and hour plus away.2) See their kids less
3) Friendships suffer. They have to maintain the strange. Sorta takes awhile for them to get back in the circle. My wife knew all of their wives. While cordial, you can understand that most wives aren't inviting the guys with 22 year old strange to dinner parties, SuperBowl parties, whatever. Right or wrong - it is what it is. Nothing in common. Try having a conversation with one where "like" isn't every other word. I see my friends a whole lot less now. Their nights or weekends are tied up. They go where the ##### is. I get it.
4) Lives are sort of hectic. Most aren't just one night stands. They get young girlfriends. Sure, sex is fun and frequent but ultimately they start pushing relationship status too. So it's probably off to the next one. Makes sense for now - why rush into another commitment, but long term they all said it's empty.
5) 50/50 on initiating the divorce. Usually cheating involved. One similar to the OP just realized they made a young mistake and weren't right for each other.
For all the no marriage types, I just can't imagine getting older without somebody meaningful to share life experiences with, and to be there if needed. But that's just me.