I’m similar to you, in I avoid confrontation. Hence me needing the advice I asked for earlier hahaha! But, if you struggle standing up for yourself. Maybe tell this person via text? Or email? This way you can type, retype and make sure you word things exactly how you want them to be worded. Also, if/when they reply, you can rehearse what you need to say in order to effectively get your point across.
Thanks! We’ve been conversing via text messages because we live far from each other. I haven’t contacted him for anything other than small talks because I’m still trying to figure out what to say and feel

thanks for the input though!
I do not want to sounds harsh but this is my two pence. Your friend has been honest and said they no longer want to do a certain activity with you for their own reasonable reasons. They have been doing this with you for a decade and are now standing up for themselves and their feelings. I think you need to seek what you got from this activity elsewhere, find a local group or online forum etc. Pushing your feelings onto them is not fair, they haven't done anything mean to you and by telling them you feel mad and hurt will make them feel guilty and imo that it not fair.
You clearly know all this and I think ultimately you just want to feel heard. If tattle doesn't settle that, do you have another friend you could vent to, about your feelings not your friend.
Ultimately this friend has not said they do not want to be friends with you, just that this activity is not something they want anymore. And I am sure you could find someone else to fill this void for you. Don't fall out with your friend over their wishes.
as much as I agree with this comment, I can’t find another group to do the hobby together because the character is his OC (original character) meaning that he is the creator, and the role can’t be passed to someone else.
probably because I’m torn between continuing the friendship or not, we don’t really have that much in common, but somehow still hangs together from time to time. That, and because I’m not sure whether I am allowed to feel mad about the situation.
Is it right for me to get mad though I understand his reason?
Is it right for me to repress this emotion and not talk about it to avoid further confrontation and to Not look like I’m being pushy?
Is it right of him to only share his opinion and not ask for mine?
Is it even right for me or do I even have the place, rather, to tell him why I’m disappointed knowing it wont change a thing?