Firstly, this kind of threads should have spoiler warning in the title...
Just a small advice to next time...
And then to your problem...
I have to mention at first that I haven't completed Hlaalu quests in a long time, so I'm mostly basing in the walkthroughs...
Have you checked the [url="http://www.gamebanshee.com/morrowind/locations/sqhlaalu.php"]Walkthrough[/url] in GameBanshee?
There are mentioned two other persons before Crassius, Odral Helvi in Caldera and Ilmeni Dren in Vivec (although you don't have to complete quests to Dren...).
Also, the following of Arethi's quests gives a hint what may also cause problems to you:
Talk to Crassius Curio
Crassius has a manor, Curio Manor, in the plaza level of the Hlaalu Canton. Head inside, turn left and go downstairs. He’s behind the door to your right. All you have to do for him is completely disrobe. Creepy. Afterward, he’ll be your sponsor, promote you to House Brother, and refer you to Odral Helvi for more quests. Technically, you can do quests for Crassius, too, at this point, but I like to get Odral out of the way first. Also, Crassius will tell you that you must get your stronghold before you can receive additional promotions, but hold off on that for now. And hey, put some clothes on.
Have you completed that "stripping" quest already? If yes, then maybe you need that Stronghold. How to get it is described in the walkthrough...