A Certain Slant of Light

This isn't exactly the same, but I've been reading Robert Louis Stevenson's A Child's Garden of Verses, in which he refers to his childhood nurse, while dedicating the book to her, as "my second Mother, my first Wife", which, as a modern reader, kind of makes me go yikes, but apparently this was considered unexceptional enough to publish in a children's book.

So yeah, it does seem like in the nineteenth century you could have both friend (sexual) and wife (platonic).