Why do we like to hurt so much?

I met him and fell for him. The first time i layed my eyes on him I ignored him smiling at me. The next few days weren't as easy. Friday came along and we slow danced... He found out I liked him a bit. The following Tuesday we started dating. He'd walk me home, we'd hold hands, hug. kiss. The basics. The 21st of September came along.. I would forever hate this day. He tells me he's leaving hes dropping out and never coming back to this town... He doesn't know if he still wants to go out. He just doesn't know. All the while my heart is breaking. I liked him soo much and he gave me butterflies everyday just thinking about him. We didn't use the L word because it was way too soon. You see all these couples using it the first day they get together. I used to too. It just attaches you more and when they leave it hurts worse than it would've. I don't want him to goo. Any advice on how to convince him to stay? I know it's his decision but... I can't lose him..