I'm sorry you're feeling badly. I've been there many times myself, and I know that simple statements like, "be positive" don't do anything to help and seem to actually exacerbate the problem.
The one thing that really helped me during my divorce was that I always had some future project in mind (generally a home improvement project) and I always tried to give it a special artistic twist that would make it different than the ordinary. That kept my mind actively engaged all the time (even when I was at work). It became an obsession, and every day, I would work on the project until I was exhausted. I wouldn't sit on the couch until I was so exhausted that I couldn't stand up any longer. I was usually sweaty, stinky and dirty, but I was happy.
I really think that getting up and moving around, even when you don't want to, is key to remaining engaged.
