я решил, запустив этот fql
$fql_areFriends = "SELECT uid1, uid2 FROM friend WHERE uid1=$user_Id AND uid2=[USER_ID_OF_THE_FRIEND]";
$friends = $client->api(array(
'method' => 'fql.query',
'access_token' => $user_access_token,
'query' => $fql_areFriends,
));
if($friends!=null){
echo 'You Are Connected to friend
}
else{
echo 'You Are Not Connected to friend
}