When he breaks your heart, he feels nothing. He moves on quickly... like nothing ever happened. You feel as if a piece of you is missing. You can't eat, you can't sleep. All you do is think about him. Wondering if he's thinking about you. Wondering if he ever misses you. You're sad for weeks, months, sometimes longer. But then you realize what's important in life, and you decide you need to worry about yourself. You soon move on, and he's stuck watching you smile. And he'll realizes he messed up.
He'll regret EVERYTHING.