He may be thinking about what it would be like to approach you and start a conversation with you.
He may be wondering about how you will react to that.
He isn’t sure.
So he continues to stare at you, lost in thought and his anxiety beginning to build with each passing second.
Guys like this are typically shy or they are very protective of their egos.
He may simply not want to put himself in a position where you could respond in a negative manner to him and as a result he may just keep staring.
Other guys who are staring at you may be thinking about whether you have a boyfriend.
Guys wonder this quite often when it comes to girls that they like.
The more attractive the girl, the more they wonder whether she has a boyfriend.
Some of these guys think so hard about this while they are staring at you that they eventually create their own conclusion.
The longer they stare without actually making a move on you, the more likely they will come to this conclusion.
They remain stuck with this conclusion.
They may tell themselves that you do have a boyfriend and thereby there would be no point in approaching you.
They may tell themselves that being that you are this attractive, you most certainly have a boyfriend.
Again, the longer they stare and do nothing, the more likely they will come to a conclusion in their minds.
Something else that a guy thinks about when he stares at a girl is whether she would find him attractive.
He may be so worried that she wouldn’t find him attractive that he may start unconsciously sprucing himself up.
You may notice him beginning to adjust some of his clothing or his hair.
He may even start picking off particles or lint from his clothing just to make sure that there isn’t something on him that would turn you off.
Something else that a guy thinks when he is staring at a girl is whether she will notice him at some point.
He may wonder if you will notice him staring at you.
He wonders what you will do if you did notice.
He also wonders what he will do if you notice.
How long would you guys stare at each other? Will you quickly look away?
Will you look upset?
Will he be able to hold eye contact for a while?
In essence, he creates the various scenarios in his mind while he is staring at you.
Now, all of these explanations have been about guys who are interested in you but are not approaching, they are just staring and thinking.
Some guys who stare are not necessarily interested in you.
Guys like this will stare and be thinking about someone you may remind them of or they may simply be lost in thought at that moment about something that is completely unrelated to you as a person.
Perhaps something you were wearing brought back a past memory and they are now caught up in their own thoughts.