ooh so many possibilities! i gave it a think and here are some options i came up with: long term vampire friend (with optional love affair), ex-lover, rival bookseller (gabriel does rare books and would make enemies with a more corporate type), possible student/teacher dynamic cuz gabriel's gonna go back to school because he's a huge nerd. if you end up having a connection with ~elysse they could know each other that way. im sure i could think of other things if none of these work for you