TL;DR, My best friend explicitly told me that "die" (the Dutch variant of they) doesn't exist.
One of my best friends keeps saying he/him and I know it's not his intention to hurt me and it's probably because of him being neurodivergent (he's not diagnosed btw) and throughout the years I've let it slide and occasionally mentioned I'd prefer die/hen (they/them) but tonight I apparently told him to many times because he said that "die" is grammatically incorrect and that "die gast" (that dude) is correct. I packed up my stuff and left the bar. My other friends joined me later at the place I'd gone to and one of them told me I had to let it rest and stop thinking about it. He's one of the most emotionally supportive of my tight friend group. And he also isn't against how I think about gender...we just shouldn't talk about it. I feel anger while writing this and I've felt invalid the whole night...is this feeling justified? And knowing myself I will calm down and wanna be around this friend again but I'm afraid he thinks he's the victim of me showing weird behavior.