When any of us are anxious, it is understandable for us to seek reassurance. It might make us feel a little better temporarily. If nothing else changes, the effect tends to wear off and feeds back into more anxiety. A good analogy is pain killer addiction: when in pain, it is understandable to take a pain-killer, but if the pain doesn't reduce by itself in the time it takes for the pain-killer to wear off, we desire another one later. And another. And possibly keep upping the dose as we get acclimatised and find that a single painkiller no longer seems to help as much as it used to.
Every time you reply to your son, you feed into his existing perceptions that he is anxious for good reason and that he cannot cope without your support. You are also reinforcing his dependence on you because he is learning, over and over again, that your own needs (for sleep, for space) don't matter and that he can expect someone else to prioritise him at all times. That isn't a sustainable life lesson.
Of course you are doing a kind and lovely thing. Who wouldn't want to give reassurance to someone anxious who we loved? So no criticism at all of you for this situation developing. Also no criticism of him as it sounds like he has been through a lot.
Just as we wouldn't expect someone to just be able to handle their pain, you can't expect your son to go cold turkey on your support and expect him to be fine. He won't be. However, unlike with chronic physical pain, anxiety can reduce by itself in the right circumstances and is not necessarily a sign of something seriously wrong. He needs the chance to learn that.
I would recommend a combination of:
- being clear with him that the situation has to change: you love him and care about him but you need your sleep and your space, and want to give him the chance to learn to soothe himself and to learn that he can be safe by myself;
- to help him prepare for the change by exploring tools he could use to soothe himself (could he have a voice note from you that he could play when needed? A voice note from himself? An anxiety management / self-soothing toolkit?)
- perhaps setting a clear timetable for the change where you start by setting a certain boundary, eg no replies after midnight, and make further planner changes from there?
All of this would be easier if your son genuinely felt motivated to change too and was on board with the reasons for changing. Ideally he would have the support of a psychological therapist who would help him to build his toolkit and take ownership of the process. It might also be that he would benefit from therapy to address trauma he has been through. But if he isn't in a place to do that at the moment, or can't get that support, I think you have to take responsibility for leading the process and setting the boundaries. As an adult it is up to you to decide what you are prepared to tolerate and what you aren't.
There is a way to do this compassionately where you don't do the equivalent of snatching the pain meds away without warning. I also think you would need to be compassionate to yourself, as I think it's very likely that your son would be upset or distressed by any process of change, so you will naturally want to drop everything and just go back to giving him whatever he feels he needs. You too might need some tools for tolerating your own painful emotions.
The rationale would have to be clear to you and ideally to him too: that you are doing this because you love him and know it would be better for him in the long-term, as well as good for you too. You both matter. Love isn't always giving someone exactly what they feel they need every time they have those feelings.
Really hard, and YANBU to struggle to do it.