Morning Scrant! Sorry to hear your S isn't well, and I do hope he's all better soon. Yes, I would agree it's a courtesy to advise of trips - but maybe that's something for the longer term as she has so little involvement in your S's care just now and you have also learned this third hand.
In terms of you feeling resentful (which I can understand). Looking in from the outside, I believe you are in a far, far better place than your W at this point. It may seem like she is good time party gal - going off with OM. And maybe she feels like that at this point. But I don't think going off and effectively giving up custody and care of your S is a happy place to be. Actually, she is giving up a great deal to be with this OM just now - and he is an adulterous man - and all of that is likely to crumble at some point and she will likely be pretty broken by that. Also, there is the guilt and misery about what she has 'done' to a good man and to her family. And if you wound others in that way, it is a self-wound too.
If you read sitches like those of RD - I think these guys who keep it all going with the family (whilst that must be tough at times) - are on a much happier path. And the kids will always know that you were there for them - and you can rest easy at night knowing that too. And this is the stuff that really, truly matters. So, whilst it must feel a bit blah sometimes with these chores to keep it all going - it's worth remembering the alternative, which certainly won't be all rainbows and unicorns, I can tell you. However, things do take time to unfold.
Anyway, just my rambling thoughts this morning and I hope your S is on the mend today.
X
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus