If youre talking with a guy and he makes eye contact with you, thats a good sign that hes into you. If hes just nice, he might listen to you, but his eyes will probably be elsewhere. But a guy giving true, prolonged, and frequent eye contact is a clear sign that the guy is interested in you romantically.

Is he flirting with me or just being friendly?

If he is flirting: A flirty guy will act more composed and cool when he wants to greet you. This is to allow you to feel comfortable with him, and if you are sensitive enough, you can tell from his gestures. If he is friendly: A friendly guy greets you the way he would greet everyone.