Both of you are players and like playing mind games with each other.
What tf is wrong with him? Why is he nice to me one moment and mean to me another?
That's the name of the game Player Hater and you allowed it.
Yep.. Either hold your ground and avoid him or confront him and say "no more"! .. He may be a slow learner, but eventually he'll get the message.
biopolar disorder?