Very simple indeed, and then the hardest part of the work is to really get how simple it is. Ironic but also amazing once we get it:)
One thing I heard about recently went something like if you accept someones negative behaviour, even if (big if) they change for the better, they would move on to someone "better" because then they basically outgrew the level of self-respect that was given in the relationship. (not sure my explanation makes sense)
Your writing resonates a lot, a super interesting topic I find!