I'm all for shipping characters, but um... consent please?
Traditionally in the Victorian era that these things seem to be modeled after, you didn't dance with the same man more than twice unless you were engaged, and unmarried women did not dance the waltz. Even as late as the mid 18th century, the waltz was considered somewhat scandalous and was even banned in some places.
So when he says "come on, it's the waltz," is he trying to establish fait accompli? If so, that's a real scumbag move.