It was also almost 20 years for me and I don't feel I wasted them. Sometimes I kick myself for not wising up sooner, but I think of all I accomplished in those years, the friendships I made, etc., and I can't regret them. Yes, I sold myself short in love and the relationship, but I am learning today to be a better person and I see everything I went through as necessary to me getting here.
As to coping, I set a time limit on my pity parties and then I got out in the world.