To think exH should've allowed DS and DD to share a room

[NamechangedAgainAndAgain123]

Me and ex adopted DD and DS at 8 and 4, DD turned 16 today and DS is 12. DS is also autistic.

He doesn't like sleeping alone and won't, he gets very upset but won't say why, I suspect it could be a fear of the dark but ive tried everything with different lights etc but nothing helps.

He sleeps in DD’s room on weekdays which DD is fine with as I've asked her and told her to tell me if she ever feels uncomfortable with this, he then sleeps in my bed on weekends as a treat and so DD can have friends round if she wanted to etc.

I have started getting him try to sleep in his own bed, I tried for the first time last Sunday and I had to sit with him until he fell asleep and he then got into my bed at around midnight.

He hadn't stayed overnight with ex for a while as he didn't want to be away from me, he stayed over last night which was his choice and when they got back today DD was telling me that my ex wouldn't let DS sleep in her room, he said it was inappropriate and wouldn't listen when DD said she didn't mind, he asks DD and DS to hand their phones in usually but when DS got upset and was asking for it back to message me he wouldn't give it to him. DD told him to sleep in her room when ex had gone to bed which he did.

He seems fine but AIBU to be annoyed at ex and for thinking he should've let them share?

I agree with you ex, it's not appropriate for a 12 year old to rely on his 16 year old sister for comfort to sleep. It's kind of her but it's not her responsibility. She deserves her own space and should learn that her own comfort should not play second fiddle to that of a man, even her brother. If he needs to co-sleep it's you and your ex's job to be the support person, not his sister.

With all due respect OP, why does your DD have to give up her privacy and space 5 days a week and this is normal, but you only give up yours 2 days a week and it's considered a 'treat'? How long has this beenhappening for? I can imagine a young girl around 13 or younger going through puberty might have found this extremely uncomfortable to have a 9 year old sharing her room when she was trying to get used to bras and sanitary products etc. And now I'm presuming DS is already or about to go through puberty too.
What happens when DD is 18 and he's 14? Or 20 and 16?
What strategies are you putting in place to make DS more comfortable sleeping in his own room? I think it's time to formulate a plan to accommodate sleeping arrangements where both DC get their own space and privacy. And if this is not possible, for whatever reason, then it's should be you and your ex who are making the sacrifices 7 nights a week, not your DD.

Also, what about when your daughter wants to move away for uni? You then have a 14 year old boy who hadn't got used to sleeping on his own and young adult who feels guilty about wanting to move on with her own life causing distress for her brother.

Quite unfair on your DD. At 16 you're making her feel responsible for him. Have DS share your room, don't unload parental responsibility onto her.

I agree that he shouldn’t be sleeping in his sisters bedroom even if she doesn’t mind, she may well mind but not feel empowered enough to say no.

Also if SS were to get involved neither of u should be seen facilitating them sharing rooms.
A difficult one for u to sort out, make an appointment with yr GP so u can get specialist help, as yr current arrangement isn’t appropriate or fair on yr d.

If being in bed with you is considered a 'treat', that implies he'd be more than happy to do that rather than sleeping in his sister's room.

In which case I find it a bit sad and unfair that you're allowing her to have her private space shared for five nights a week, at a pivotal time for her development, while you only do so for two days a week despite being the adult.

If you don't want him to sleep alone, and he's happy to share with you, why is her room the default rather than yours?

This.

I don't think they should be in the same room. I expect dad was trying to protect everyone.