I don’t know why you’ve dropped everything in your life but him, but I can tell you that’s not healthy. You need a life, hobbies, activities, friends, etc to feel good and whole and useful. You aren’t exercising those things, so you feel useless. The walks are a great start. That’s how I started after I was last really down. Small steps. Make a to do list of simple shit you do everyday to adult. Like:
I like lists and they make me feel accomplished so that stupidly also helped me. Or writing down what I actually did all day when I was thinking I was useless and occupying house space…I would actually be doing things between the wallowing.
I hope you can call an old friend, even one you’ve lost touch with and maybe feel a little better.
Avoid online relationships, I think I read somewhere that 2/3 people saying they are single online are actually dating people or in serious relationships IRL.
You need in real life connection to other humans. I hope you can get a session or two with a counselor or therapist, there’s more than lining after an internet person you don’t really know?