It takes time to stop obsessing, and probably more importantly, having a replacement obsession can help immensely. Home improvement projects did the trick for me, but I stumbled into it, I didn't do any planning. I noticed that one of the vinyl shutters on my house needed to be replaced. My next thought was, "I hate the crappy, fake looking vinyl shutters." Then, the thought after that was, "I can make some wood shutters." And that's what I did.
In hindsight, my home improvement projects kept me sane. As I went along, I took bigger risks, both from a construction perspective as well as from an artistic perspective. Those projects became all-consuming mentally and physically. As bad as things were, it was also really good; I had tons of fun with the projects and the house looks fantastic. I was still a good dad, but during those times when the boys were away, I had something to occupy my time and my thoughts.
You need to find something other than your marriage that can consume your thoughts and your time. Just get out and start doing things; you'll find something that you'll enjoy.
