Soozi, I'm sorry about DH's health issues and hope he is much better now. Also, I'm so sorry about the problems w/ your YDS (youngest dear son). Whatever "bad things" her remembers from his childhood, unless abuse was involved (and I'm not getting that impression), I don't understand how he can still be holding it against DH after the man has suffered 2 strokes! Mindboggling!
Are there any particular issues between him and DH that could be resolved. If so, does DH feel up to working on them?
Regardless, what an awful position YDS has put you in - rock and hard place - get to see him and leave DH behind or stand by DH but lose out on seeing YDS. I'm not sure what choice I would make. Usually, I would stand by DH, hands down - wouldn't even have to make a choice, it would be obvious to me. But, IMO, it's a more difficult choice when a DS or DD is involved.
Hmmm... I THINK in the end, I would, generally, stand w/ DH, taking the position that we're a team, a package deal, etc. However, if I thought DH had caused the rift or was being too stubborn to do what he needed to do to begin to fix the issue, then I might focus on salvaging what I could of my own relationship w/ my AC.
Then again, I see mumofmadboys' point. But that's something I'd have to talk over w/ DH. If we agreed that my seeing YDS might lead to his seeing both of us, in time, then I might go ahead and see him w/o DH. But if DH said he would feel ostracized, etc. as Namsnanny mentioned, then I wouldn't. It would be a joint decision between DH and me even if it were not a joint visit.