Most Helpful Girl
It's hard with a sticky situation such as yours here, dear, because with you both living in the 'Same apartment complex' and you not even beginning to lick your war wounds yet, it Is going to be hard when you run into one another.
Try and avoid This at any cost. Stay clear of her and don't let her fruck with your life or get a chance to. I imagine she still has a few wounds of her own that are healing, being you both were together this long.
It will be normal for her to get uptight when she runs into you. You both shared history together and she probably is Missing the Kissing.
For now, stay away and if it is meant for you both to end up as friends in the end, living in the same building may be the way to build this foundation and even Rebuild... another relationship, who knows.
Next time you do happen to cross paths, don't let on this bothers you and play this guy who is doing just fine... it might get her to thinking of what a good catch she lost and get her attention to have realized just what she lost.
Good luck. xx
Most Helpful Guy
The short answer 1: find another love. You're young. Sometimes, it's a shit and love hurts when it is broken, but the pain will diminish as time goes by.
The short answer 2: focus on your studies, career, sports, spirituality, everything that may lift you higher and busy, avoiding the thoughts about her (yea, they may still remain for a longer time, but they will not drag you down like they're doing now, and someday you will be able to even talk to her, if it is the case, and not be down for it).
Love yourself more: you will overcome it.