first of all got to drupalchat.module file
Add define this variable DRUPALCHAT_REL_FL on top of this module

<?php

define('DRUPALCHAT_REL_FL',		3);

?>

go to: function _drupalchat_buddylist

Add the line

<?php

  elseif ($drupalchat_rel == DRUPALCHAT_REL_FL) {
    $result = db_query("SELECT * FROM {friendlist_statuses} WHERE requester_id = %d AND status='%s'", $uid,'TW_BOTH');
    while ($friendlist = db_fetch_object($result)) {
     $users[] = $friendlist->requestee_id;
    }
  }
//placed before return
return $users;
?>

Then open drupalchat.admin.inc file

Then place the code in the drupalchat_settings_form

<?php

// line 86

 if (module_exists('friendlist_api')) {
    $form['drupalchat_rel']['#options'][DRUPALCHAT_REL_FL] = t('Friendlist module');
  }

?>

Done!!!!!!

Go to admin/settings/drupalchat

change Relationship method.