How do you cope with the lonely times?

I suppose this is a little bit of a vent, but I do find it comforting to see there are folks in this sub with similar problems to mine who seem to have found their happiness. If you have any advice, hit me with it. I’ve been doing the single dad thing for about 4 years now. I have dude full-time. It's a blessing because his mom is a mess, but it's also tough. I don’t know that anyone should have to do parenting alone. I do pretty well for us all things considered. I went back to school and got my degree. I busted my ass and have a good job that gives me flexibility to parent. We live by family, so there is help. And my son, though exhausting, is a good kid. Things could be so much worse, but lately I am just really struggling to find my happiness. Maybe I’ve just run out of problems I can control, and I’m feeling a little stuck. I had developed feelings for a single mom friend of mine. First person since my son’s mother. Good or bad idea, it happened. She didn’t reciprocate, and the friendship fell apart. I’ve never felt this alone and unsure of what to do. That probably sounds silly, but maybe you all understand. Meaningful relationships just don’t come around all that often in my situation. I really need a new avenue for seeking out my own gratification and happiness, but I am just having trouble figuring out something I can actually throw myself at as a single parent. If you’ve read this, thanks for listening. It’s good to have a reminder that it isn’t an island.