I cant add certain people as a friend and when i press add it unfriends me a second later

I am trying to add my friend, kevin so i can add him to my realm. i search him up and i click add, and a second or two later, it unfriends me. i have tried LITERALLY EVERYTHING!! i click on his profile, and i click add friend, and nothing happens. i have signed out and in of my microsoft account, i have played without the microSD card, i have tried restarting my switch, but nothing works. he has been unadded for over 2 weeks now, and he is really mad and frustrated.