I think you should just ask him. Guys are really hard to read, and only he knows really how he feels. Take matters into your own hands, and just say something like (not in these exact words “I really dont get you lately, you ask me to prom, and say oh well i dont know if im going _____ (whatever else you want to say). If you like me or dont like me then tell me. Youve made fun of me and then you ask me to prom and then say ‘Uhhhhh i dont know if im going anymore” and i really dont know what to make of it” or something like that.
hopefully that helps! 🙂