BuddyPress.org

Accepted:

Use the do_action hook in function friends_accept_friendship in this file:
buddypress\buddypress\bp-friends\bp-friends-functions.php

function my_accepted_function( $id, $user_id, $friend_id, $friendship  ) {
  // do something
}
add_action(''friends_friendship_accepted', 'my_accepted_function', 1, 4 );

Removed:

Use one of the 3 do_action hooks in function friends_remove_friend in this file:
buddypress\buddypress\bp-friends\bp-friends-functions.php

Which hook you use depends on what you want to do.
Create a separate function to hook to; something like ‘my_remove_function’.