he stares at me and smile?

it is never for sure that simple. But there definitely is a certain tendency. There are type of behavior that more often mean one thing than not.

From my own personal experience I can tell you that looking at and smiling a girl is a very good indication that a guy at least finds you attractive. I try to be kind by looking at and sometimes even smiling at people in general, which is the one thing that you have to be careful about, but girls that I really consider good looking and/or who seem to have a personality that I enjoy get MUCH more attention through eye contact and smiling than the typical girl.

In your case, I would definitely have to go with him being interested in you. Especially since the gazes are so long and frequent.

If you think he is cute, then you should give it a shot. Just start a friendly conversation when possible with him. You may be like most girls and think it is okay to wait and make him do the heavy work, but a lot of guys have difficulty getting past that first phase of being interested in a girl. So, while he may be more than willing to start a conversation with you, if this looking has gone on for some time now, then he might not have the guts to actually be social with you. Since guys can tend to be a bit too interested in looks, you can be wary at first, but definitely at least try talking to him and see how it goes.
Source(s):
I'm a guy. I look at girls. I smile at them. Girls I am interested in are definitely treated in a different way than those who I don't have an attraction to.

Nope, you might not have screwed.
Talk to him personally and apologize and begin a casual talk.
And about the nodding to another girl part, don't worry, he did that to avoid being embarassed :)

Yes, he will stare and not be able to do this..

You screwed up

Now all chances are lost. Next time smile back and wave