When do they/when have you come back?

I’m 41 out of my first serious relationship. I was told this past Saturday that my ex has a bf and she wants to some how remain in contact but we can no longer be in contact we used to be. We existed in a grey area for two years and I thought she was “the one” but I guess she felt differently. At the moment I do hope she double backs, it obviously wouldn’t happen any time soon but in your experiences what usually causes someone circle back and is it likely to occur? The way I’m feeling now I hope it does happen but obviously it’s not in my control at all and I’m already doing my part to move on with dates and what not.