site_url and $current_user producing undesired results

You are just missing the concatenation operator. Your code should look like this:

$buttons['Edit My Profile'] = site_url('/forums/user/') . $current_user->user_login;

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)