So , you're in love ...
do other things , such as playing games , talk with other ppl , ask what the other person wants to talk about , because if start the convo you'll remember that person that you're trying to forget.
try to go outside. don't do something stupid =) and more importantly , don't drink alcohol and don't eat too much
Edit: if you run , like... practice running or if you go to the gym , then ... when you go to run ... you should just go with the flow and not really over-do-it because of the emotions that you have right now.
and when you go to the gym , you should really try really hard in the weights that you're lifting ... but not over-doing-it =) , plus when you're in the gym you shouldn't try and lift heavier weights that you normally don't lift ... but instead of trying lifting new weights , you should lift more harder and with more determinations the weights that you use to gain muscle , however , you shouldn't over-do-it =). and more importantly , you should be cool with your friends and not try to run them over because of how you're feeling =).