just because ye dated other people doesnt mean you are not gonna miss him. you probably do.
is that how and why he got dated
Doesn't mean anything except something that happened brought him to mind, probably subconsciously, and the thought triggered the dream.
As I said, it was probably something subconscious, maybe even just a sound or a scent that stuck in your mind until you went to sleep.
I'd say it meant nothing except that somewhere in your mind he still has a place in your memories.