I try to keep the "life is what you make it" mentality strong. Doesn't work 100%, but as long as I keep repeating this concept to myself, I've seen improvements. A few years ago I went to a conference at the suggestion of a friend. The topic covered strong personal control, and leadership of self rather than others. Simply put, you can't control others. But, you can control your reactions and feelings about what happens.
Depression from diabetes is tough, real tough. Keep up the best things you can, and try to laugh when you can.