not keep in touch with after breaking up where I wonder what had happened to her. (I didn't keep in touch with many, but I was engaged to this one and always wondered how things turned out for her.)
Over time, I think I only remembered the good things of the relationship combined with not having any kids made things really easy. When she connected with me on Facebook a long time ago, all of the wondering and fondness disappeared completely and made me even more grateful for my wife.