Quite a few of us have divorced a similar type, bullying and narcisstic so seek out support. YouTube has some excellent resources on escaping and recovering from toxic people, some by qualified professionals.
It is very common for "victims" to lash out eventually and your thoughts are discussed in Lundy's book, "Why does he do that". Have you read it yet?
A few things, that I learned, he will react very badly to feeling out of control. He maybe fairer in the divorce settlement if there are mutual people in your life who he wants to maintain an image with otherwise he is unlikely to be fair or reasonable. He will genuinely believe he is the victim, such is his sense of entitlement that equality feels abusive to him. He is unlikely to be capable of insight or introspection so there is no point attempting to influence him.
A good phrase I learnt and tried to practice was "observe, don't absorb". So when he starts to dominate, try to detach yourself from his reactions, almost like you are watching a toddler throw a tantrum. At the same time do a quick scan of your body, e.g are you breathing heavily or holding your breathe.I find this helps to achieve grey rock.
Later down the line if communication is limited to email never respond immediately always give yourself time to process. These types are masters of manipulation and will try to trigger you to gain a reaction.
The only things that matters to him is control of you (or his son), having his agenda met or maintaining his image (which is as a victim and Mr Nice Guy).
The 50:50 is very typical as he knows giving up being main carer will hurt you and secondly it helps him achieve a better financial settlement. At 12 your son would not be forced into that arrangement. Would he stand up to his Dad about this?
It is rare of narcisstic individuals to manage without someone to provide attention/adoration so if he is "letting" you go be prepared for another woman to appear very quickly. At this point your son is likely to be dropped as 50:50 will not suit.
Finally, it takes a long time to heal from an abusive relationship but it is possible and life will be much better for you and your son. The more that my children spend with their Dad the more they realise how toxic he is, they tend to return home drained which is sad to see but at least they are not living it in all the time.