I don’t know who I am when I’m not in a relationship

I have a problem where if I’m not in a relationship, I don’t know who I am. Whenever I’m in a relationship I’m in a really good place with myself, I’m happy and just feel good. But whenever I’m not in a relationship I feel so shitty and lonely. I don’t know who to be when I’m not in a relationship. I don’t know how to be enough for myself. Any advice on being comfortable when not being in a relationship? I need to be more dependent on myself, if that makes any sense?