With my exA it was something very small that finally allowed me to let go. After 4 years of mental abuse, neglect, womanizing, lying etc. (which should make you walk away). It was a picture that he put on his fridge of another woman's daughter.
I knew about this other woman. He was back and forth from me and her for the last year. He would be at my house and texting her and yet I stayed.
But, recently, He moved into a new house. New house maybe new beginning. When I saw he put the pic on the fridge. I got in my car and left. Have not seen or talked to him since.