You should feel really good about all you did with endurance sports. I have a similar story but with yoga. When I was depressed I couldn't drag myself to go, even though I knew it would make me feel better. Finally I started going once a week for a while, and then upped it from there. And wouldn't you know it, I started to feel better! Maybe start with a walk around the neighborhood? It sounds like being active brought you a lot of joy, purpose, and stability, so I would try my best to start slowly and see what happens! Definitely not easy but it will be so worth it. Baby steps!