This may not be the answer to your long term situation, but sometimes when I feel sad it’s because I am spending too much time thinking about what’s missing, or gone. When that happens I remind myself to make lists of all the things that I like or love about my life. It helps me remember how good life is. It doesn’t even have to be all that great. For me something as simple as, the taste of and crunch of a green apple, or the bite of can of icy soda lead to better and better feelings. Eventually it becomes people I love and all the great things about the world. It’s deceptively simple but it really works for me.