OP I really DO sympathise, and am sorry if all the suggestions are frustrating you.
I've suffered chronic depression for years. It lands on me, like a massive wall has spring up between me and the world I want to live in. It got so bad that I was bedbound for a year,. In that year I achieved nothing at all. No social life, failed mature student uni, earned about 6k all year. I felt like a lump of gristle that didn't deserve to breathe.
I decided to take an entire year out of my life. Commit to nothing (except bare minimum work to get by) and try anything and everything I could to feel better. I did. It took four months before I felt anything at all. But by May I was starting to feel alive, by June I was active and dynamic - making proper changes in my life. By september - there;s no point in saying because it sounds like a trashy movie, but the most incredible changes had come about, stuff I couldn't have dreamed of.
Life didn't stay that good. It dipped back down. And it's wobbled along ever since. But I know what to do now. I know what can and will work, and I won't ever let myself feel that useless and pointless and valueless and disappointing to the world ever again. I blew opportunity after opportunity, lost so many friends and colleagues because I was so lacklustre. But now life is good. It really is.
You have the advantage (from the sound of it) that you don't have any children at the moment, so you don;t have that responsibility. You are free to dedicate a lot of time to yourself, to feeling better, stronger, happier, more in control of your life and what you wnat from it. Whenever you feel ready to hear this - whether you believe it or not, you can make changes.