I put the word 'Ended' in quotes as for me Harry Potter never really ends.
But really, I've not looked forward to anything as much as I did the next Harry Potter book, or the next Harry Potter movie. The mounting excitement, going online and discussing the Ifs and Whats and then finally reading it/seeing it. If read a few good books, watched some movies but I've never really go into anything as much as I did this. I wish I was creative and write some fanfiction (as i love reading it) or drawing some fan art or joining a wrock band but really it's left a big void in my life! Is there anything out there that can take the place of Harry, Ron and Hermione? Or, am I doomed to live the rest of my life with a piece on me missing?
To sum up. Just how has everyone filled that hole?
I toy with fanfic ideas on a regular basis, even though I don't write them down.
I regret that I missed out on some of the fun while the books were still coming out, as I didn't get to discuss them with anyone.
Rewatching the films, rereading the books, reading Rowling's newest stuff, on Pottermore, and just moving on with life in general. I have other interests. I always have. HP will always have a place in my heart, but it's ended and I have to graciously accept that.