Hm, I think that it means pretty much what it says. They broke up, and it's eighteen days later. It kind of sounds like the person he was with wanted him to be someone that he wasn't, and left him. He's been trying to change, but it's not exactly easy. And it's been a while since he's seen her, spoke to her, or held her. He just misses it. He wants his other chance.
Or maybe that's just me sharing my exact situation with you all.