You poor thing, it sounds very hard. Is he sitting his GCSEs this time? What does he want to do post-16. I know it is probably little comfort but there will be parents out there whose children are extraordinarily violent to them and are not attending school.
I have a girl with ASD a bit younger and probably not as threatening but who can be very dogmatic and rigid, plus I do have a supportive partner, your ex sounds awful. We never go into her room, I try to respect her space as it’s a need for control with some autistic children, she brings out her clothes/plates at times, it’s a tip but then she has a blitz.
Advice from Camhs, when our relationship was at its worst, was to keep lines of communication open via texts, try to drop most demands at the mo, if he’s doing exams as he will be under stress at school, just try to keep stuff light and breezy, don’t get drawn into arguments if you can help it, pick your battles, try to look after yourself and keep your own life going outside this relationship. With my girl I would just send her funny stuff via text I’d read online or memes occasionally, make her little gifts sometimes of sweets etc, it’s sounds counterproductive, like rewarding them for being so vile. Although She is still quite troubled, our relationship has improved a lot.
you are doing a good job, this time is not forever, there are a lot of parents of NT and ND kids who are struggling and most come through it. Look after yourself