Who read the last GG book? Who is Gossip girl? With whom Serena and Blair end up?

You still don't find out who Gossip Girl is. Both Blair and Serena are singel when the book ends, however the book is meant to covers(xmas and new Year)3 or 4 years in which Serena dates Nate and Dan and Blair dates Nate, a guy she meets at school named Pete and my personal fav Chuck.
I think the book ends with hope that there may be another...