Should Social Media Rules of Engagement for Marriages and Relationships Vary?

Over the years, I've seen a number of relationships and marriages go through changes as results of social media activity, but after reading a recent article, I became a bit more curious.

A person wrote to an advice columnist:

DEAR HARRIETTE: I do not like to bring social media into relationships because I feel like it is a bit childish. However, my girlfriend has recently done something that bothers me. On a Facebook post, one of her ex-boyfriends commented, "I miss you." On that same post, one of my friends commented, and my girlfriend responded with a kissy face towards him. I tend to not read into social media too much, but my girlfriend is acting like she's single, especially on this post. She ignored the ex-boyfriend's comment, but I was still rubbed the wrong way that she didn't delete it. My girlfriend hasn't said anything about the post, and I haven't brought it up. I am not sure if I am being dramatic or have the right to be suspicious about the whole thing. Why is she being so flirtatious and leaving up messages from exes on her posts when she's dating me? -- Puzzled, Westchester, New York

Here is the columnist's response:

DEAR PUZZLED: Rather than blowing this out of proportion, speak directly to your girlfriend. Tell her that her ex-boyfriend's post made you uncomfortable and that you don't know why she left it up -- or why she posted a kissy face at her friend. Tell her that it makes you feel like she is flirting with him, which disturbs you.

Ask her if she misses this fellow. Probe to see where she feels you two are in your relationship. This could be "innocent" flirtation with the push of a button, but without much thought. Or it could point to a bigger issue. Talk to her so you can find out.

I've seen married couples share one account so that there are no secrets or misunderstandings. Initially, I thought that screamed "insecurity," but being on the outside looking in, I realized you never know what a couple is doing to prevent unnecessary issues or to get over something that happened but shouldn't have.  For some couples, staying together is harder than it is for others.

However, in matters of relationships, I don't think having joint accounts is practiced.  But I have seen where couples decided not to be "friends" online once a relationship has begun so as to not become jealous of the attention the other half may be receiving. "Why are you friends with your ex?" "He/she said you were cute and you didn't even try to set it straight and let him/her know you're involved!" That issue may have been addressed privately, but even if it wasn't, how is it disrespectful for a person to note that your partner is taking good care of him/herself?

In the letter written above, the writer says the girlfriend acts like she's single. (I'm not even going to get into the whole "if you're not married, you're single debate.) Does not flaunting your relationship equate to "acting single?" What do you expect of your other half when it comes to social media?