The most horrid thing is you'll never get an answer that will give you closure.

You just won't.

Voice of experience here, the best you will get is understanding that there is just something...broken or missing in them, that is not in you. You'll learn concepts like emotional immaturity or generational trauma or maladaptive habits or projection or a whole bunch of other ones but they're just puzzle pieces you constantly juggle around, there's no one piece you can one day point to and go AHA! THAT WAS IT!

Because it's not you. It was never you. It's them. And you can't process another person's psyche.