E. M. Forster's Maurice and Edward Prime-Stevenson's Imre, both fiction about gay men written in the Edwardian period, both use 'friend' to mean 'romantic-sexual partner' in ways that seem to be playing with the equivocal meaning for deliberate effect, and it's something I like very much about both of them. In Imre the phrase 'the friendship which is love, the love which is friendship' is repeated at several pivotal moments (sometimes with Significant Capitals).

All of which is to say, it's a really interesting question! (as is the question of changing ideas about types of love in general, really). I didn't know that 'friend' was sometimes used between (heterosexual) actual married couples—that makes it even more interesting.

your friend you haven’t had sex sex with but you definitely share a bed whenever possible and kiss each other’s faces while murmuring fond words of deep emotional attachment. —hahaha, excellent summary of a specific sort of 19th C Thing...