I have seen this in several places, and different people have different reasons for it. But from the viewpoint of someone (perhaps me) who is trying to get a message through, I have to wonder if the spouse or boyfriend/girlfriend got the message when the intended recipient was the other person. I also have to wonder which one of the duo is making the comment on Facebook or wherever.
I used to have this problem before Facebook existed, and before many of my friends even had email. Why? Because of "Southwestern Bell Call Notes." This was the digital voicemail service - for those of you young enough to have never had a landline phone - that the local phone company used. Users were able to make one account or several, so that the caller could pick who they wanted to receive the message. This effectively rendered the service no better than telling the phone answerer to write down a message. You have to rely on that person to get the message through.
So I've had this question for a while... Why? Why can't folks have separate accounts? Are you doing it so there will be no secrets between each other? Because it's not difficult to make up a new email and open a new social media account if somebody did want to keep secrets. I don't want to freak people out. I just want to know why the rest of us have to be subjected to the weirdness.
This is Shelli talking. That's my name up there saying this is my blog. I approve this message (until someone changes my mind).