I still struggle with this myself so this is one of those cases where I really should take my own advice. lol I do understand how you are feeling though.

When you think of the good times do you feel maybe he was a touch smothering? A little too nice?

They learn to hide it. They pretend to be this awesome person when they first meet you because they've learned along the way that most people don't like their usual personality.

Then because they know of your past struggles and self doubt they use it against you.

They get into your head and convince you that it's all your fault after all you admit you have issues. They've never needed therapy so it must be your fault.

Or they're only mean to you so it must be you bringing it out in them. Don't fall for that one either if they aren't treating someone else badly it's only because they haven't suckered that other person in enough to show their true selves.

It's not you. It's him.