I'm mildly upset with my so for playing fortnite
Do you mind if I ask why you're upset with them for that?
I hate him for wasting his time on such stupid games like fortnite.
In your view it may be stupid, but many others love Fortnite. You shouldn't take away your partner's hobbies that he enjoys. Would you like your hobbies shut down because your partner dislikes them?
That's not the same. That's adult stuff. I don't understand why he can't do something productive.
Just because you don't think it is productive, doesn't mean it isn't for him. He could be doing it to wind down as a hobby, and if it makes him happy, he should do it. Why don't you try joining him for a game, he could teach you and you'll have fun together.