You need to select all records from User_Music table except musics for the current Userid and all users that are in the friends table for the same user.
Suppose if you are looking for music recommendations for a user UserId = 1 then the query should be like
Select * from User_Music
where UserId <> @UserId and UserId in (Select FriendId from Users_Friends where UserId = @UserId)
Hope this helps!