When the bomb was dropped, I wasn't really thinking anymore. My thinking was done over ~12 months before I decided to leave. As I was leaving, I was concerned for my H and how he was going to cope with my leaving. I said a lot of stuff to try to make it easier, like I never loved you.
As for what made me reconsider - it started slowly - first I missed my friend, then my lover, then my husband. I began to see that I had things to work on, not just him. I started to see him confident and happy. I knew something was up when I started to hope that we'd run in to each other. These feelings started about 3 months after I'd left and took about 3 months to fully develop.