Is it who you are or are you hoping by being nice to him he'll be nice to you? You seem hung up on when he is nice and when he is mean. Never mind he is a lying cheater no matter how he is treating you.
It sounds like you have a case of Nice Girl Syndrome. Look it up, it is a real thing. And could be explored thoroughly and get you over it in IC.
M(53), W(54),D(19) M-23, T-25 Bomb Drop - Dec.23, 2017 Ring and Piecing since March 2018