Is it normal that i can't stop caring

So its been over a year that my gf of almost 5 years left me while i went away for med school. While i was there i really only had her as a crutch for support. I pretty much went from school to home and would call her just to leave the phone on while i studied. But at the same time even before i left i knew her friends were pulling her away from me because they didnt care much for me and at the same time she would delete conversations she had with guys on her phone and gmail. In response i got paranoid and started telling her not to do things or dress a certain way (which was totally uncalled for). In the end she waited until a really busy week in which i had four exams to dump me. I begged for her to come back but she refused and was going on dates less then a month after. As i thought back to the way she was and from other people telling me I guess she was cheating on me towards the end. Well i came back to town a few days ago and tried to reconnect and she responded to every text but she blew me off when i asked to hang out. I don't know why Im still head over heels for a girl that cares nothing for me and is chasing other guys (the guy she left me for dumped her). Ive been in many relationships after her and casually dated and regrettably casually slept with lots of girls to try and get over her. None of this is who i am, i never did these things before and i dont care to. but its the only outlet i have since im moving around state to state since im on rotations. Any advice on how to move on? she has consumed my thoughts everyday for the last year thinking about who is she sleeping with, flirting with., etc.. i want to move on but i feel stuck!