I think it's the support human role which is tiring me, though it is - on one level - less crucial as my adult stepson lives with his partner. And I had been managing as a very part-time support human. It is not that onerous to make dinners and express interest in someone else's life. There's just mild irritation at never being asked how I am/what I'd doing and all the conversation being about his life and his interests.
What tipped it for me was the recent meltdown where there was outpouring of rage and aggression about my alleged role in his terrible sufferings as a boy. This has coincided with his recently becoming a father.
I really don't know if stepson has been harbouring these feelings/memories for several decades and 'masking'. There's little evidence to suggest that he has done - for example he's always been happy to eat the meals that I cooked and never suggested to his Dad that it might be nice for the two of them to go out somewhere (eg the pub?) instead, sometimes.
It seems a bit more likely that the feelings have been around but in a rather minor way ie he had these memories but they didn't really bother him. But now they have erupted because he is a Dad himself and wants to do things absolutely perfectly for his vulnerable bag - and it is now intolerable for him to think that he received anything other than perfect care when he was vulnerable young person.
Meanwhile before the baby was born there'd been this assumption that I would a) continue to be a support person for him and b) a support person for the new baby - though of course not one that made any inconvenient remarks or actions.
I think there is also assumption c). Yes, my stepson had this huge meltdown in which he attacked my present character and past treatment of him. But he also likes routine and things always being there for him. So I suppose in his mind, he has simply told me something that is objectively true - and that there is no reason why I (despite being a cold, yet over-emotional, abuser - should not continue to have him to supper and help take care of his child, if/when asked to do so.
Life, eh.....