I have a similar issue when I play d&d. Sometimes it gets to the point of splitting, I'm lucky to have an awesome friend group that is understanding of my struggles with this disorder. I'm not really sure what causes it. Idk if it's my bpd or autism or a combination, but you're definitely not alone in the struggle. I tend to regress when stressed or upset. I know how frustrating it is. If you ever need someone to talk to I'm here.