Oh man, Andy, Im really sorry to hear that. I really am.
Im always worried everytime I go back to see my family, in the town and city I grew up in, that Im gonna be recognized, and people start gossiping.
I actually think it was good of you to call over that guy and talk to him. Hes probably thinking "->-bleeped-<-, I shouldnt have done that". Why on Earth he felt it was his place to say, I dont know.
I know from what I and others are saying, you are getting conflicting opinions on what to do, overall it is up to you, what you feel is right for your situation. But I think maybe you should speak to her. Maybe not over facebook, she may respect you talking to her directly. Is she someone who you feel is a nice enough person? i.e not a gossip/bitch...? Because maybe you could just speak to her privately, casually and calming and just be like, yeah, what he said is true, brief explanation, bla bla bla, but youre just Andy now, nothing else so youre asking her not to go round telling others.
Like others have said, its best not to panic, or show your panic. Despite how much it must be raging inside you!
I hope all goes well for you mate, I really do.