you posted some serious question whose answer is central part of healing journey for many of us.
There are many reasons why we are left fragile vulnerable, feeling isolated from others and under such conditions that many times we are trying to reenact experience that could be similar to original abuse comparing destructive forces and submissive feelings - that is my perspective.
To say it by simple language - it looks like some demons are left which are taking control from time to time over our loves and many years later.
Your topic reminded me of one another that I've seen just recently and there I wrote something that I would like to repeat here.
So here is the link
maybe it would be helpful for you to read it.