OP: I left a 21 year relationship similar to the one you described. Good times, peppered with emotional and verbal abuse (once physical), 2 wonderful kids, alcohol dependency, anxiety issues, depression.
It was the hardest decision of my life, clouded with fear, doubt, guilt and obligation. You see, for some reason i still love the bastard. I left 3 months ago. I left my beautiful home we built together, I have disrupted the kids lives, I have cried more tears than you can imagine.
He won't believe its truely over, and to some degree that is my fault, because I am trying to keep things as amicable as possible. He keeps love bombing me, then reverting to type when he doesn't get the response he believes he should have, and turns nasty and angry again. Yesterday I visited some mutual friends and told him, he was pissed I went. I knew he would be, he feels left out, isolated etc. He is still trying to control me.
The best thing he could have done was tell me he understood why I left, give me space to work on my own issues, and remain pleasant but distant. Of course that was never going to happen. If he had done that and shown me he was making great strides towards dealing with HIS issues (that he projected onto me), IF......there might have been a tiny tiny chance. But all he has done has cemented why I left in the first place.
His behaviour over our relationship has left me with anxiety ( i am a happy go lucky person usually), low self worth, disorded relationships with other people, and a whole heap of ongoing thoughts about what I deserve and don't. You will have damaged her beyond your imagination. She has shown huge strength of character to leave you and you should be proud of the mother of your child for that.
The best advice I can give you, is try remain amicable, deal with your issues and do not expect anything. If she moves on, deal with it. You had your chance. You need to unpick what happened so you don't repeat the same mistakes again and show your child what a strong father is, who respects all women in his life.