I remember back in my college days before I started dating my wife, I started to get close to a few worldy girls. We'd hang out between classes. When one started flirting with me pretty heavily, I tried moving things to the next level and she let me know that wasn't her intentions at all. Same thing - no boyfriend, dressed sexy, flirted, commented on my sexy looks. Fortunately, we stayed friends.
I chalked it up to Jehovah protecting me, but I know different now.