Literary version: Perhaps everyone has, in the passionate, bewildering days of youth, loved someone with all they had. After giving too much, they realize they may never be able to throw themselves into love the way they did back then again. Perhaps they were hurt, perhaps those days are long gone, and the people from that time have grown into someone else.
Brief version: The male lead didn't know how to cherish what he had. He's an idiot, and then he comes crawling back. That's the story.
Crazy version: A bunch of people making a melodramatic mess of things. (Is it really okay for me to try this hard to ruin the synopsis?!)