He is talking about a nameless girl (because according to the author he likes make things ambiguos or vague). Sara Tapes is just the name of this extra content, but Wirt keep talking about the unknow many times that means that his content only can be interpreted like a sequel.
He talks about the unknow and the people who live there (how ideal he considers them and the place) and he keeps talking about birds and how he miss Beatrice ending it asking himself if she will remember them now that they are separated.
Wirt never stop of being Dante (the character), he is separated of Beatrice but they will be reunited again eventually, this is how goes any story based in the divine comedy. (Men, even Dante Inferno is loyal to this part with the "Goodbye my love..." but we know that they will met again)
Come on, even the author is a WirtxBeatrice shipper since he boycott the relationship of Wirt and Sara.