You've made me want to visit Anglesey, even as you had me feeling as if I was visiting these places with Severus and Harry.
I'm not a huge fan of "miscommunication" as a plot device, but you brought me into just the right place in their miscommunication and you made me believe that they just didn't think to talk to each other. It felt like a natural result of their personalities at the time it happened, not something forced onto them because of the story.
I was mesmerised by their journeys -- physical, emotional, and psychological. And the ending was simply perfect. Excellent work. This story is going on my rereading list.