Welcome black cat!

I think at some point you have to just make them be independent! E.g They MUST sleep in their own room - he has to know that there is no other choice! If he comes out, take him straight back.

I told my DD she had to learn to make her own breakfast but she didn't want to- insert argument- every.single.morning.. Until I just said if you want to eat breakfast then you make it or else go hungry - I'm not arguing with you over YOUR breakfast!! Haha.

It's so hard not to just tear your hair out in frustration!
I've had this argument for 5 and a half years, we will be doing it until 6 am, I know because we've done it before, and not just one night but we tried consistently. It sounds simple in theory, but ds and what I presume is separation anxiety won't have a bar of it, and when your the only one around and still have to work and function everyday. *shrug* yep I created a little monster. *sigh*