Good question, Golden Eve.
It’s a combination of our own flaws/pathology and that of the abusive other person that drew us in.
Take my friend for example; my boundary line that she crossed was way too generous. I should have ended that friendship when she wouldn’t stop taking jabs at me. I confronted her and said she better stop with the jabs, and for a while she did. In hindsight, I’d have been more wise to simply end the friendship at the first jab. I never take jabs at my friends, so why did I put up with it from her?
I’ve been reading every article I can. Like, “How to have a healthy relationship,” or “How to spot a narcissist”.