When you really like a guy, you might incorrectly interpret his actions, because you're seeing things the way you want to see them. That means that even if he hasn't been flirting with you at all, you'll assume that he has been. Of course, you don't want to twist his words and fool yourself into thinking that he has feelings that don't actually exist. You need to be careful, because it's easy to mistake these things for sexual tension:
If he's staring at you, then yes, he might like you. However, he might've just noticed that you've been staring at him and is looking over to figure out why. You have to be careful, because you never know what his glances mean. He might be admiring your sexiness, or he might just be trying to figure out what on earth you're doing.