The control of your friendships is entirely in your hands. Within your character's smartphone menu, click the button with two faces to go to your friends list. There you can:
Accept or reject new friend requests;
Search for your friends, if you have their full nickname (name + #numbers) on hand;
Add people who are playing in the same world as you as friends by clicking on the search icon;
Delete friends in the "My friends" tab if you want to make room for other people or do not want to be visited by a player;
Visit online friends.
Your friends don't have access to personal information about you or your account.