Anyone taking on a new partner with teenage children, needs patience, boundaries, extremely good humour, and skin as thick as a rhino. Teenagers are often angry at life in general, even when family is still together.
This is all so true regardless of whether families are together or not. However, taking on a teen has a lot of complexities.
My dd was dating a 16 yo boy for a very short while, whose dad has recently remarried. I have heard his mum was super super strict but has had to back off completely as he has refused to obey the rules anymore, shouting, swearing etc.
From what I’ve heard from people, who know the family, he sounds pretty angry about it all and has displayed some self destructive behaviour, getting drunk and going off alone etc. He got expelled shortly before his exams - private so the the threshold is much lower and would not have happened in state. He is also seeking the thrill of having more than one gf at a time, stringing girls along etc.
Idk what this boy is like at home but he’s manifesting his displeasure in life imo. Just the things he is doing are different. I oscillate from being really annoyed about how he is treating girls in general and feeling sorry for him.
I get being accused of hitting a 16 yo is serious. However I hope my little anecdote gives you comfort that this isn’t about you, but about him, rather like chasing my dd when this boy already had a gf and snogging a 3rd girl, negging my dd then dumping her was not about my dd at all.
Now that this has become serious, your dh really needs to sort this out, maybe get your dss some therapy if he’s that angry. But please do remember that much as he’s big and powerful he is still very much a kid and hopefully he can come out the other side from this and will realise his behaviour was awful.