Why did he tease me so much?

Okay there was a guy at work that I used to have a really big crush on . He had a girlfriend at the time. He would tease me all the time he wouldn't tease the other girls just me . I never did anything to him Every time I would talk to other guys he would say that they are going to stand me up or their numbers are not real . We would always have these play full fights. We were total opposites . Every time I would talk to him he have this bashful smile on his face . I don't get why he would get jealous if I talked to other guys for? He broke up with his girlfriend in dec and he left the job in feb . He still comes in once in a while . I finally got over him but why is there a part of me that thinks about him all the time for? am I really meant to be with this guy?