So, for him, it was only ever transactional.
You get him, in his cock-lodging glory, but in return you have to be “a family”. Being a family means he can try to get your child out of your house, but you look after his 3 under-parented children, including the one who is hostile to your child.
That must hurt, but at least you know.
He really thinks he’s the bee’s knees, doesn’t he? That he’s worth your house, your space, your parenting resources yet you aren’t worthy of small acts of affection like walks, morning coffee.
I keep saying this and I’m sure you are sceptical - I too thought parents were exaggerating about the teen years - but 3-4 teen children is a lot. His children with ASD/ADHD are more likely to struggle and he’s not a great dad, is he?
He’s not a catch. He’s probably got 2 years max to try to convince someone else he is, until the upcoming teen storm. And when that passes in 10+ years’ time (assuming they leave home) he won’t be so young and handsome then, will he?