It sounds to me like you decided the relationship wasn't working for you when you had your "fling."
The best way to know if you still love someone is, once limerence has passed, ask yourself if you have all the components of "healthy" romantic love, which according to one theory (Sternberg) is commitment, intimacy, and passion. Your story lacks commitment, so I'm not surprised you're unaffected by her leaving. It sounds like you already had one foot out the door.
http://en.wikipedia.org/wiki/Limerence
Oh, and P.S. You sound like you're starting to walk down the path of serial monogamy.