I'm not really an expert, because I haven't had to deal with the work aspect as well as ds's SENs...BUT, I do know that home schooling turned ds2 around, and what had been complex needs became less complex. He was out of school for two years, one of those years, he had part time tuition at a very small tuition centre which specialised in learning difficulties, and he was beautifully behaved there. And it was only a few hours a week. But he learnt focus and study skills and how to enjoy being in a classroom with a few other students.
I don't know if your son is on any medication for the ADHD. There are various threads about this if you search on Mumsnet.
There are also a fair number of threads where anxiety is mentioned as one of the reasons ASD and ADHD children misbehave at school, and the frustration for them of being asked to do things they cannot, and that overflows into home life.
When you are a square peg all day, conduct disorder tends to follow. Whereas a child is away from the place that doesn't suit, some of those aspects of his behaviour may improve, AT HOME, with you, and it won't be "festering".
Ds 2 spent a lot of time outside running around, and meeting children from families where there was a mixture of ages, in a non judgemental way when he was home educated. We didn't do that much formal work, but a little, just to get his confidence back (he was dyslexic)
When he went to the tuition centre he did a lot of art, which previously he had disliked for sensory reasons. And enjoyed it.
He went back to mainstream state school in a much better state of mind, although he still needed support (we organised an EHCP when he was out of school)
8 is a really difficult age, and it seems to be when the developmental lag really shows, other children are beginning to obey orders and focus at lessons, and your child isn't and isn't communicating in an appropriate way with other children, so socialising is very difficult for them, and frustrating. they get left out of games. Their confidence is so low. For us, home ed built up ds's confidence, and stopped me needing to wait for him to come home and explode, because he stopped exploding!!!
Your partner seems to be particularily insensitive here, what he needs to be doing is support you in whatever decision you want to make, and above all to support your son in your home, not want him out of it. But if there is a school that does suit and there ARE weekly boarding schools; certainly NT children go to them...
I wouldn't have wanted ds to go one; building the bond between us, helped his behaviour, whereas sending him away would have created a new problem, our relationship might have suffered. In a funny way, going through that difficult period together has made me in an expert in how to help ds2. and he has come out the other side more independent and better able to deal with OTHER people.