You're not stupid.. you are however a hostage to his behaviour. It's like stockholm syndrome; you love what you remember is the good of this person, you empathise/sympathise/hope it will get better, saner and it is difficult for anyone not in the position of hostage to understand why you don't just call a halt to it. Breaking free is hard. And peversely, breaking free without some catastrophic event to force you free is even harder.
I've been there. I've had friends saying wtf and I've said you don't understand you just don't get it. I've had people say, I'm scared for you and said it'll be ok.. he's not THAT stupid/insane/whatever.
I've also felt frustrated with all the 'it's simple just leave'. It isn't that simple. It's frightening.. it's the unknown.. it's taking steps that are scary along a path that is unfamiliar into a tunnel you can't see the end of.
Keep posting. Keep documenting. Keep telling people. Keep safe.
Tx