Hi Bananahead
You're really not getting anything out of this relationship now are you.
Abuse as you are aware is not just physical in nature but psychological as well. He has in all truth done a right number on you and has likely manipulated you gradually and throughout your entire relationship. He is truly a master manipulator and he targeted you as well. What did you learn about relationships when you were growing up?.
re your comment:-
"He is a very driven, sociable man and very generous in many ways. But he has the emotional IQ of, I don't know, someone I have never met before and he is quite narcissistic. I know all this. I also know how difficult he'd make my life if I left and my youngest daughter would be caught in that and I can't bear that idea, which is why I stay".
Your life is already difficult in remaining with him (and in turn his overbearing controlling mother). He is not generous to you is he; many such abusive men are helpful to those in the outside world. It is behind closed doors that their true nature emerges and your friend you write of has stated you are not being oversensitive here.
The above is a frankly terrible reason for staying, you're basically saying that you are staying because of your youngest child. Staying for the kids rarely if ever works out.
How do you think she would feel knowing that you stayed with your dad because of her, she is really not going to say "thanks mum" to you for doing that to her. She will likely call you soft and daft for staying and she could well accuse you also of putting this man before her and her siblings. Doing that could also harm your own relationship with your kids going forward because none of them will want to come home to see you and dad, if you are still together then, when they are adults.
If he is a narcissist in terms of personality then he is an appalling example of a parent to his kids. He is no husband to you and you are being completely trampled on by both him and in turn his mother (like mother, like son here). How dare he treat you like he has done to date.
You really do need to get this bloke and his attendant mother out of your day to day life. The two of them between them are really making your life an utter misery.