Uninterested first relationship?

I had my first romantic relationship last year with a girl I had been interested in for a long time. I wanted her, and she wanted me...and then we started holding hands and kissing, and suddenly I didn't care any more. At all. It was weird, because I had secretly lusted after her for ages, and once I found out she was secretly lusting after me too, it was like I couldn't be bothered to get it together and just make out with her. So we had a bizarre, practically platonic relationship, and then we just ended it, without any tears or anything. And now when I see her, we smile and act like we never had any feelings for each other. What do you guys think?