There should be a maid standing around in northern Trademond, near the guard compound. That's Arwin's house. If she tells you Arwin isn't at home, you can't (and don't need to) talk to him yet. I think you need to enter the Congregation building for him to "go home", which requires an event on the northern road (marked with a !) which in turn may require fulfilling a number of quests.