So my trans cousin made me go really sad…

Let’s give some info before starting: I have a cousin, this year he told me “hey I’m trans” so I accepted him. Let’s call him Gull

Gull and I always were like best friends forever, the problem is that I’m feeling horrible by the way he treats me. Sometimes when we are talking I call him a “she” by accident and he tells me “if you do it again I will stop talking to you” or tells me things that really confuses me. Today he I called him “she” again by accident and he told me that he would stop talking to me, so I decided to tell him like 

“chill, you know I accept you the way you are and I’m trying really hard call you by he, don’t treat me that way for some text error of mine, is hard after this whole years, also I don’t even know how to call you, you never told me and when I call you by your surname you tell me ‘you only humiliate me’ and you make me feel of course bad”

He only replied that I’m talking nonsense and to call him like his friend does… IM NOT AN GUESSER TO GUESS WHICH NAME YOUR FRIEND CALLS YA

Also he said I was downgrading him. That’s real nonsense.

I told him “I’m not a guesser, also I’m trying hard” and he just said “fuck1ng nonsense but you really made me hurt” LIKE? YOU ALWAYS HURT ME BY THE LITTLEST THING AND I SHUT UP BECAUSE I ALWAYS TELL YOU YOU TREAT ME WORSE, HOW?

I’m the wrong one?