Well, hello captain obvious...Try loading a save or an autosave from before you chose to go down the Peitho path.
Yes I could just not start the route, but seeing as I've put some time into the route I'd rather not waste it. I've no idea if the route is a one way street or if I've reached the end of the current content. If it is a one way street the Devs should make that clear before you go down it.
The reason i went down that route instead of the ambush route, is the ambush route gave a warning to finish everything in town first, and trying to do that put me down the Pethio route with out any warning that I couldn't get back.