I DON'T UNDERSTAND HIM?

When i was with my boyfriend, the guy i had a crush on my fresh man year started reaching me flirting with me, one night around three in the morning he messaged me on FB telling me he "missed me" , this is the guy who graduated and left me hanging like a dumb - *** over a year agoo .. was trying to talk to me, rite after me & my ex went down hill and broke up, he asked me on a date, but left me hanging ? a few months later we ran into each other when i was with some friends , i quickly wanted to run away so fast and hide but i didn't i acted like everything was normal, and spoke to him, he had the nerve to ask me if my best friend was my boyfriend, i quickly said yes to see his reaction and than told him no that was just my friend, he quickly got relaxed when i said no! now we don't talk at all, i don't understand him ! Now what do i do the next time i approach him?