Had this happen before. I was with a chick for 5 years and she just started changing mentally for the worst. So, I left her. It was still hard to just ditch her like I did, but I just got anther chick to hang with and kept me busy. Another time, this happen to me the chick left me and I was a litle crazy about it. It took a few weeks, but I just stayed busy and flirted with every chick possible. Ended up not talking to her for 6 months straight and she came back. It is very hard to get over emotions. It is crazy how much you do not want to feel that way but it happens without control. Like everyone else said, stay busy. It will help keep your mind off of her and eventually you will forget about it.