How can I stop feeling like I need a relationship to be happy?

So I (21M) was ghosted by a girl I’d been dating a few months back. It hurt me a lot at the time, as she was the first girl I’d ever dated, but I’ve been feeling better. I still think about her a lot, but I can look back on it more objectively now. The pain has, to an extent, gone away.

What hasn’t quite gone away and, in fact, has gotten worse due to the pandemic is my desire for connection with someone. I’ve never officially had a girlfriend and I’ve always been teased that, of all my friends/siblings, I’ll be the last to settle down, if at all. It’s always been something I’ve been a little insecure about. I’m worried I’m just not compatible with anyone.

At this point, I feel like I’ve heard everything. ‘It’ll come when you least expect it’ or ‘Focus on yourself’ or ‘Work on yourself first’. The list goes on and on. While I have been more positive and I have been focusing more on myself and my own happiness/success, I find that I’m still thinking about if/when I’ll ever be in a relationship every single day. I alternate between two states of mind, it seems, where one day I’ll be happy that I’m single and the next I’ll be lonely and sad. It’s gotten to be a little exhausting.

My question is, how can I truly and genuinely live my life without thinking about this SO much? I’ll go through bouts where I’m happy being single, but how can I sustain that long term?

Thanks everybody!

TL;DR: How can I stay happy being single and stop thinking about if/when I’ll find a girlfriend?