Why do I want to go back? Why did I stay?

Abusers hijack the "resolution and repair" pathway in the brain. Our brains are socially wired to seek repair in case of social/relationship damage after an argument.

It was beneficial for organisms to survive in groups (e.g. thousands/hundred of years ago), and the ones that did get to live on (rather than being eaten by a tiger in prehistoric times, for example). In current world it's not always beneficial, however the inherent drive is still there.

Abusers hijack this evolutionary pathway by never providing a satisfactory resolution, thus keeping the "victim" attached to them by wanting to get resolution.

The pull to connect with a social group is very strong - stronger than life actually, as evidenced in people going to war and dying "for the group."

TL;DR; You were sticking with it and staying due to some evolutionary mechanism that prevented monkeys from being eaten or dying alone in the cold in prehistoric times.

You're going back due to some evolutionary mechanism that prevented monkeys from being eaten or dying alone in the cold in prehistoric times.

I moved on by realizing the protective mechanism I explained above and thinking about it from time to time.

There's zero shame in being a victim of abuse, and it's OK to learn things as we go. That's all humans do. I'm glad you're out.

Technically, you had no conscious control - you were going on subconscious decisions without analyzing the situation consciously from viewpoints that helped you move away. Once you started analyzing the situation from different viewpoint that you had before, you moved away.

By doing what you already started - thinking about the situation, seeking different opinions, and analyzing it, you're exercising your ability to think consciously if a similar situation happens in the future. This is healing.

One goal of healing, in my opinion, is to shift from subconscious to conscious control in situations that are emotionally loaded. That helps analyze them in the moment (or as soon as possible after) and respond in ways that are healthier.

Hope that helps explain it.