What happens inside their heads is anyones guess. They detach b/c they have to. I think it's self preservation for some, they literally have to go. It is too painful for them to stay. When someone is truly miserable, they try to find a shread of happiness however they can. I think this goes for alot of folks not just MLC.
Do you get to see it? Not necessarily. Even if you do, you might misread it. That's why we have to let go too.
As far as Thanksgiving goes, you do what's best for you. The trick is watching your expectations. you can't tether your boat to what they do.
I can tell you that up until this year, I always invited my H and he always came. The difference this year is that we (D's and I) were invited to a friends and we've opted to go. Did he ask about coming up? Yes. Does it mean anything? Not really. In my case it means he's trying to stay connected to D's. the problem is, as of late, my D16, doesn't want that connection. She will find the path to him that works for her.
