I am so confused please help!

I am so confused please help!
I am friendly to guys but I don't have any intention. I know a guy and I think he is a good friend and I think he is quite friendly to me too.but all of a sudden his friends call me stocker! I was so upset and I assumed that guy might talk about me behind my back! Now I don't even know how to still talk to him. Also what does it mean when someone said you are just one of the cooperators?