I agree that this varies from relationship to relationship.
At my job we have a saying, “Never put anything in an email that you wouldn’t want to see as an exhibit in a legal proceeding.” I feel confident that I could engage in roleplaying with an anonymous Size acquaintance without forming an improper emotional attachment, but I wouldn’t want to have to defend the transcript to my partner.
I’m much more comfortable keeping to my current practice of writing stories with one or more Size acquaintances in mind and hoping they eventually figure it out.