I actually wonder if M regrets marrying H. He's not LA level wealthy and the royal gig was far less fun than she probably imagined at the outset. Her husband's family are not enamored with her and then there's the press, critical and ready to catch them out for every misstep instead of adoring and positive.
I also wonder how they're getting along, isolated together all day everyday. It's a strain for everyone and they don't seem to me to be people with much in common in terms of life experiences, culture or interests (outside of performative philanthropy).
Obviously this is baseless musings about two people whom I have no special insights whatsoever, but I do wonder if M wished she'd been able to bag a billionaire like Serena's DH to really enjoy the lifestyle without the critical press coverage.