How do you build up the strength to leave the man you love?

He clearly doesn’t love me.. He doesn’t even care if I were to leave. But the thought of leaving is agonizing. How do I just stop caring like he does and build the courage to walk away without needing a back up man? (That’s usually what I do when I try to get over someone.) I don’t have friends either so “going out with friends” isn’t an option. Please help.