I would have a talk with women’s aid and also, a solicitor. Find out how to get a favorable divorce. Confide in any supportive friends too (not anyone who would go behind your back and talk with him).
You are absolutely right about getting out as your boy is picking up the abusive behaviour. Which, is actually him being abused too btw. It is abuse to a child to witness their mother being bullied.
He will find it harder to turn his son against you if you aren’t there to be part of the abuse.
Keep reverse psychology in mind. This man means you harm. So he will want to hurt you. I would make a song and dance about how he needs to stay in his son’s life and you really need him to do his share of the parenting when you split up. Make it seem like you want him involved. Really “I’d be heartbroken if he didn’t get to see you often because we spilt” ham it up. That way he will be more hands off just to spite you.
Which is ideal. Because the less time he spends around the child, the better.
Do not compromise on anything you don’t want to. He will not be kind. He will simply take the compromise as weakness and move the goalposts, demanding more.p or something else.
I know you are scared he will turn on you but, he already has. He is already a viper. Do you want to die by a thousand cuts? Do you want your son to grow up to become the same monster as his dad or, wind up in an abusive relationship himself because it’s all he knows?
Get your ducks in a row and talk to the solicitor first. You would be wise to have someone else with you when you tell him it is over. Be prepared to call the police if at any point he becomes aggressive.
It will not be easy but you owe it to yourself and your boy to get away from this horrible man. Your son deserves one emotionally safe household he can be in with you as much as possible.
Be prepared for the manipulation tactics. Look up “narcissistic smear campaign” and “narcissistic hoovering”. Be aware he might threaten self harm (if he does this, call the police and let the handle it). Do not be manipulated.
Have a get out quick bag packed incase you have to flee the home. Once you have told him you are finished, never share a room with him again. If he won’t leave the house, make sure your bedroom door has a lock. Or consider staying elsewhere.
Put the sale through on the home as fast as you can.