This is a very interesting discussion.
For what it is worth, here is my pound's worth:
I was the one to walk away, never wanting to see the man again (it was a futile, hurtful relationship with no romance whatsoever), and I genuinely felt my heart was broken.
I left him, spent 6 weeks away on work trips. He collected me at the airport and to cut a long story short, once he had overcome my considerable resistance, we married and produced two children, and over 20 years later we are still together.
We are total opposites in every way, and that makes for a lively, interesting, worth-working-for relationship and we are committed to making it work.

Regarding your person who wants out and to be totally, completely free of you. I can understand your wanting to understand what happened and the motivation behind it. You are willing to learn from previous mistakes. Why not go quiet and genuinely ask your True Self a few questions. Stay open for the answers and accept whatever you get, no matter how it comes. Ask questions like, a) What can you learn from this? b) Why did it happen? (people are not always clear or honest about their personal motives - maybe you did nothing untoward?) c) What do you personally need to do in order to let go and move on gratefully/gracefully? d) You seem stuck in the past with this issue, ask yourself how to move into the present.
Good luck and here is to genuine growth with no holds barred. I really hope you get to the bottom of it and can move forward in total self-acceptance and freedom.
Adieu, French Claire