Look for the "Forum Jump" menu at the bottom of this page, right-hand side. You can use that menu to navigate to the various boards here, and the "Dating & Friendships" board is on that menu list.
Also you can go to the main page -- http://www.polyamory.com/forum/
-- and scroll down to where it says "Dating & Friendships." Then click on where it says "North America," and go from there.
Let me know if you're still stuck.