I've heard many times that if a guy looks directly in you eyes when you talk to him then he likes you. If it's true, then I don't get it. because what else is he supposed to be looking at? I think it's normal that when you talk to someone you look him/her in the eyes.
I don't think it means anything when he is just talking to you, it is purely polite to look at someone in the eyes when talking to them, its pretty disrespectful for someone to be looking about when they are talking to you. Different if a guy stares at you or gives you eye contact when he isn't talking to you... from a distance or whatever.
When someone is talking to you, looking them in the eyes is what your suppose to do. It lets them know you are listening and paying attention. If your looking for signs the he likes you then pay close attention. See if when he looks in your eyes if he compliments them or if he smiles alot. But you are right, this is normal behavior.
It depends. It is polite to look into the eyes of the person you are talking to. The point where it becomes excessive, like when you start to feel he's staring at you and you get uncomfortable, is when he likes you. Or conversely, when he glances at you for only a few seconds, is also a sign that he likes you. So basically, an average amount of looking into eyes is polite, too much or too little indicates attraction.