HELP. Does a girl touching a guy's hair mean she is flirting with him? Or could they be friends?

I've seen these guy and girl together all the time but no real physical contact except that one time. They usually don't seem flirtatious. But I have seen them talk to each other one on one while the rest of their friend circle was jabbering away. Though I do like this guy, and I have seen him avert his eyes from this female friend and stare at me while talking to her.