Depression

Any suggestions on how to let go of past regrets. I've been clinical depressed 3 times in my 54 years. Every time it starts with reliving past regrets and dwelling on how I should have made different decisions. My current situation isn't all that bad, just in a job that I don't like with no future. I was employed for 14 years with a large airline but laid off in 2001. I constantly dwell on how if I had made different decisions I would have been able to keep my job back than. It haunts me night and day. I've been on Cymbalta about 4 months and feel better than I did. Just want to let go of the past and move on, but the rumination just won't go away. Any suggestions?