I was thinking about this topic just now. Trying to process. So glad you posted this. it is helpful to hear from others when they knew it was time. I posted a thread a long time ago that was even titled i think it's time to leave or something like that. The "I think" was crucial there...Obviously I was tricking myself still.
For me there was the 'i think it's time' moment, but then there was the "I KNOW it's time" moment that broke me, broke my spirit, dashed my hopes, and told me I must repair myself. It was a moment where I took care of her and got nothing but abuse in return. I'm dealing with other things now related to no contact and lack of closure, but for me...
It was physical violence toward me and fear of it escalating to something more intense in the future. My hopes for the future were dashed after she hit me repeatedly, in multiple ways, in public and not in public, in a single night that was supposed to be a quiet early-Christmas goodbye before I flew home to my family for the holidays. Telling her 'I love you with all my heart' during her blackout and getting hit in the face as a response. Carrying her home and learning she did not recognize me or seem to know my name. Her trying to kick and punch the owners of a restaurant that same night - all out, full-body, put your full weight into it punches... as people watched with their mouths open. Like a movie or a nightmare out of body experience. Her trying to lie in the street after the restaurant kicked us out, in some half-hearted suicidal demonstration (would not call it an attempt).
This is just a minor percentage of the mega-dose of things I saw on the night that finally 'got through' to me.
The day before this happened, we exchanged christmas gifts and she made christmas dinner for us. It was one of the most beautiful things I'd ever seen, one of the most beautiful things anyone had ever done for me.
The violent night would have been enough, but the juxtaposition of these 2 emotionally intense days was so heartwrenching and confusing. But I knew I had to leave. I thought I might die if I didn't.