If there is a guy that you think is in love with you, make sure to approach him first and befriend him. That's because he won't have the guts to do so because of his personality or past experiences. But how do we know if he likes a girl or not?
Shy guys actually make things really simple for girls. If you are a girl and you've come across this guy who feels shy everytime you meet him then he likes you a lot. Try to talk to him and find out the kind of girl that he likes/dislikes, his favorite movies etc and you'll understand him more.
Most shy guys can be really complicated to understand. They might like a girl and still not openly confess their feelings towards them. Other times, they could be in love and might even talk about it openly on being encouraged by others. In short they are really unpredictable and you should not take things for granted. Your best bet would be to talk to them openly or read the signs being given out by their body, because shy guys are very good at exposing their internal feelings by means of body language.