What is this guys problem?

so this guy gave me so many signals he liked me but honestly i never gave him any in return. now he has a girlfriend. do you think its possible that he did like me and he didnt know i liked him so he just moved on? and if thats the case then if they break up do you think he could go back to liking me? i really like him but was too shy to do anything and figured he would never like me so never took the things he did as signs but now lookingg back. we've never talked in person before if that makes a difference