I jerk off to the thought of my friend even though she's taken

So I've known this girl for 3 years and I was about to seal the deal with her recently until she was asked out by another guy the day before I was going to take her out. And I'm good friends with this guy. But before he and her started dating I had gotten a few chances to check out her body, mainly by looking down her shirt, which showed off damn near all of her boobs, which I've had so many dreams about. And I still jerk off to the thought of her and I having sex. Is that normal?