vent + asking for advice

Okay, so there is this one person in my class who is trans I think (I am not sure because I don't really know which genders are in trans spectrum). So they go by any pronouns and recently changed their name, not legally but they asked everyone to call them Ariel.

This is where the problem comes, I am really bad with remembering names, I don't know 50% of my classmate's names, but I know/remember Ariel's legal name. I accidentally deadname Ariel sometimes, but I always try to make it up as soon as someone tells me or I notice I deadnamed them. I know this can be really bad on Ariel but, they now started yelling at me whenever I deadname them. I hate being yelled, it kinda scares me and I quickly either shut up, hide somewhere where I am alone and sit quietly or start bursting with emotions. Ariel KNOWS IT. But this is not the end, Ariel get's mad when I deadname them but deadnames and missgenders me on daily, they didn't even gender or named me correctly once. I do not usually have much of a problem with people calling me by my birthname or using my gender assigned at birth, but this is a different case. Ariel knows I want them to call my by my chosen name and what pronouns I prefer. They are treating me like a shit and yet they get mad when I deadname them, say sorry and correct myself. I don't know what to do about this all. This is not really good for my mental health. This whole situation is making school, a place where I felt really free, seem like a hell to me. I notice that I am less likely to talk to anyone even if I want to and that I am slowly shutting down.

Please give me some advice. Things like talking to adults or changing schools are not avilable to me. I am in the closet and I really like my school. This is the only not homophobic and transphobic school around me.