Guys are so weird and I don't understand why he did this to me? Lingo help please?

Ok so I'm a sopre and this guy's a freshmen right? We have been really close back in middle school and have been. I just found him in the first day of school at the lunch area. I told him It's been a while and he's like yeah it is. Then he went busy talking and laughing with his friends . Then he asked so how is your sopre year? I said okay-ish yours? He said yeah its cool then again went back to his friends and later ditched me O_O;; . We used to talk like hella back in middle school!! What happened here?! :( I asked my friend what it means she said "Probably because he's in a bigger step (high school) and hasn't adjusted to some of his other friends that maybe he's confused a bit for a while. And to give him time" But I still don't get it.