I can't fell happy when my heart is broken. please help me!!!?

I recently broke up with my first girlfriend, and I just can't get her out of my mind. I mean I just want things to be normal again like before I got a girlfriend and before we broke up. but I can't do that when I miss her every second I live. I don't hate her or anything negative about her. Im just really heartbroken and really love sick. we don't hate each other or nothing like that just I feel like shes avoiding me? its probably a good thing because shes trying to get me off her mind. we have only dated for 2 and a half weeks but it fells like a way longer time because I liked her way before we started going out. so if anyone out there can please give me some help on how to get over her and get back to normal like it was before and some tips to prevent this from happening in the future, I would really appreciate it. please my friends think im gonna turn emo and im having breakdowns at night.