I realised I was the passive person and my ex was abusive. It's a horribly crippling place to be though as their abuse pushes and pushes you into a person you don't even recognise. I did escape, I did realise that it wasn't ok. But 10 years out of the relationship now and I am still learning to stand up to him in a safe way.
And of course leaving didn't make the children safe. The court eventually ordered contact despite compelling evidence (medical, police, school)
If your enabler parent had left with you but then you had had to spend weekends alone with the abusive parent (a v common scenario these days ) would that have been better or worse? If we try and say too much about how abusive the parent was we run the risk of being accused of parental alienation and losing all access to our children