AIBU to not invite my 20 year old son on a trip with his siblings?

I think this feels harsh to me. You’ve said you don’t want your children to pick sides but as soon as he opted to stay with his dad you ‘went quiet on him’. He was experiencing a huge change and loss of family life, not longer living with both parents or with any of his siblings. Then to reach out to you and you not actively respond as you would have before the separation must have been painful for him. I think you should have tried to make the effort with him more, I know he is an adult but he’s still young and you’re the adult parent in this scenario. I also feel that by doing this you’re pushing him more towards his dad and fracturing your relationship with him.
taking his siblings away and sharing photos online must have been really hard for him to see. Yes there are some issues between siblings at the moment but is there any scope for you/their dad to support the sibling group to work through this together?
can you spend some real quality 1:1 time with him too?

It’s not about having low standards for kids, it’s about having high standards for myself. What you, and others, seem to be saying is that being hurt isn’t an excuse for lacking care or thought for the 20 year old? So why is the (understandably) hurt mother given a freer pass? No one has behaved brilliantly, again understandably. But one person is fully mature and the parent and so should lead the efforts on reconciliation.

I think, when the OP said "He's still my son and I love him. But he's also an adult who chose to stay with the parent who broke this family" she is definitely punishing him for not picking her side. It's not the right way to go about things.

Your husbands affair isnt your kids problem. Yes it hurt you understandably but hes still their Dad. He cheated on you not them.
Imagine if your husband chose to ostracise the 3 children who chose to live with you.
You are causing the problems here by treating your eldest son differently because he chose to live with his Dad. That isnt him saying that he agrees with the affair.
You're upset but taking it out on the wrong person here. Your son is retaliating to your behaviour. You're distraught by son of the things hes said but hes distraught that youre excluding him. You're pushing him away. Sort your relationship out with your son before it's too late!

You’re right, ideally 20 year olds should not hit out at their parents even when they’re hurting. But the same logic applies equally, or in my view more, to parents not hitting out at hurt kids. When you “go quiet” ie ignore your hurt child that is not ok.

I think you've behaved terribly. Your ds is not to blame for his father's infidelity and it's horrible to punish him for maintaining a relationship with his df and staying living in the house that's familiar to him.

It's harmful to all your dc that you're requiring them to choose between their parents and siblings in this way.

You can be furious with your ex, he's a shit, but don't hurt your dc.

No one is "pleased" with the fallout of the father's awful betrayal of his wife and children. Perhaps people here might have felt slightly less inclined to try to repeatedly present a different perspective of the OP's son to her were it not for the multiple posts calling a young person they've never met Andrew Tate, vile, controlling, misogynistic, narcissitic, incel, obsessed with "daddy's phallus" etc. etc in the direct aftermath of the collapse of his parent's marriage and the family set-up. You're not actually interested in helping the OP reconnect with her son. You've made that very clear. This is about your issues, not hers.

No. But I would understand that as the safest person I was being lashed out at.

I would talk to my kid, might even yell. I wouldn't cut him out.

Yes, and it's deeply hurtful.

Daddy can have an affair, but heaven forbid he's blamed for destroying the family. Let's blame mummy for this.

Oh, please. Male entitlement at its finest.

Would you be pleased if your children blamed you for leaving your cheating partner?

Have to agree to disagree there, I think telling any woman, never mind your Mum that it's her fault the family is getting "broken up" after her husband has had an affair and she's dealing with processing that is pretty vile actually.

"spewing vile filth".

From OP post he lashed out at some point that his mum had broken up the family. Later he said he didn't want her to date. Both of these intemperate statements stem from hurt, fear, distress at his certainties in life being torn up. We have no idea what he has or has not said to his father on the subject as it is not recorded.

He also "reached out" to his mum on more than one occasion, which suggests olive branch or at least neutral attempts to get in touch, suggesting that he wanted to make amends.

The argument about the graduation was between he and his sister and other than him being hurt we have no idea what was said.

I don't think that counts as "spewing vile filth". I do not think it warranted his mother ignoring his attempts to get in touch, and I don't think it warranted being excluded from a family holiday.

I don't think cutting out your adult child because they said "hurty words" in a time of immense upheaval is proportionate or good parenting. I think it reflects extremely poorly on this mother. That doesn't mean being a "doormat". It's not cut them off or be meek and mild. Tell your son you won't be spoken to like that. Tell him it's hurtful. Making out there's no middle way is just ....ridiculous.

I don’t know what’s worse - that you purposely excluded 1 out of 4 children, or that you simply “didn’t think” to invite him.

Grow up, you’re the parent here. I think you’ve got a lot of apologising to do.

What do you disagree with?

Bloody hell, aren't you a peach?

The OP needed a break from her son, who was spewing vile filth.

A mother is not a doormat.

It would be strange if that's what she was doing, but she's not.

It seems very strange to be openly punishing your child for not picking your side in the break-up. He shouldn't have to do that. You should be communicating with him surely - including pointing out the parts where he's being unfair and unrealistic - and trying to find a way to get your relationship and those between your children back on track?

I don't think many people today truly think all 20 year olds living at home with their parents are grown women/men. Many are young adults with growing still to be done. The OP ignored his repeated attempts to reach out, took her other children on holiday and posted photos of it that he could see. Is that how grown-ups are supposed to behave?

Whatever. He clearly blames his Mum for something that wasnt her fault and decided to stay with his Dad on this basis. I can't believe the people here making excuses for this grown man.

Are you ok?

Totally agree

I wonder if the posters criticising the "grown adult son" have maintained the same level of maturity as they had at 19/20? Im nearly 40 and I'm pretty sure I have matured significantly and am probably an entirely different person now compared to me at 19!

Eh? Nobody has said anything goes. Nobody on this thread has said it’s ok what the eldest son has said. What a strange take.

What posters are in fact saying is that what the son has said is not to be taken all that seriously particularly at this dreadful time. When everyone is terribly hurt, is finding their way and or has been excluded and isolated.

Thanks to the marvelous father.

And posters are also saying that at this dreadful time, the op should not be going quiet on her son at all. Quite the opposite. And certainly not excluding him from trips regardless. She should try to be a port in a storm for all of her kids. Ofc she’s suffering too. That is the nature of the affair beast. To put everyone through the wringer.

But the op is the grown adult here and she is being cruel and distant to her son.

My DC have said some thoughtless things in their time. They have even, heavens above, lashed out verbally when upset or under stress. I’ve always tried to understand where it’s coming from as, to be fair, I would with my friends, colleagues and wider family. But I’ve never ignored or isolated them.

I’m bemused by the red flag misogyny that people are seeing. The OP has brought him up and he has two sisters - if he is angrily anti women, one wonders what was going on in the house before March. I think it much more likely that his world was falling apart, he was trying to make his mum and siblings stay put and he was expressing his very real fear of being displaced by a second family. No where does OP say he defended his father’s actions - his reasons for staying put in his own home were probably complex and again, OP doesn’t say where or what type of living situation he was being offered if he chose to go with her.

Anyway, it doesn’t look like OP is returning but I do hope some of these replies have made her think about her DS’s perspective and they can move forward.