I would wonder about the usefulness of it for relationships that weren’t primarily conducted via text for the whole duration of the relationship.

Almost all of my relationships have a pattern in texting. There’s usually a month of deep and emotional conversations, followed by a few months of sexually explicit chatting as we spend more time together and work out the emotional conversations in person, and then logistical conversations once we’re emotionally and physically comfortable with each other. And sure, we’re kind and sweet to each other between the logistics, but I don’t know if that’s really enough to train an AI on, or even enough to properly represent ourselves or the relationship.

I think that any AI would have to be very advanced to not respond to “Why did you leave me?” with ‘Because I had to take the dog to the vet/go get milk’ or whatever - especially when the bulk of the texts are in that latter relationship stage.