Most Helpful Guy
Some basic shy guy signs are, he avoids unscripted social situations (casual conversation), he gets nervous or panicy when making long conversation sometimes breathing extra heavy or sweating, he often finds or makes up excuses to leave unscripted social situations.
The reasons for this are not a reflection on you or weather or not he likes you. They are a reflection of his lack of social skills, and the fact that many people have taken this to mean that he is rude in the past, which only compounds the problem because he always feels like he needs to be the best conversationalist, but he has no idea how.
Also, he may be very outgoing in other areas such as at work/school or with close friends, and be shy with you. This is because is social skills with women are not where the rest of his social skills are, it may also be that he likes you, which intensifies his anxiety, because he doesn't want to screw things up.
Is there any guy in particular you are wondering about?