I can relate and think these feelings are probably pretty normal in these situations. When you've been with someone so long you know them inside an out. The good, the bad. The wonderful, the ugly. The strengths, the vulnerabilities. At times it does sort of seem like you lost two separate people. And I think as time passes we sometimes forget more of the bad and remember more of the good. Sometimes I can only think of the good part of the woman I left behind. And the heartache I caused her. And it's just absolutely devastating. I worry for her. I want her to be okay. But at the same time I know there were a lot of problems and a lot of it (not all) was her fault too.
It's been especially hard for me during the holidays. I'm constantly reminded of the good times we had. Even when things aren't great, people generally tend to at least fake it around the holidays. So all of the memories of the season are so wonderful and joyous. And I long for them. But the rational part of me knows this is a bit of an illusion and only half of the story.