For me I have witnessed a huge mixed bag.
When I was in a long term relationship, I posted pictures of us and when I was drunk I would every once in a while gush about him, but not that often. And this was a happy, healthy relationship.
I know people who are unhappy in their relationships, so they don't post a word or a photo of them or their partner at all.
I also know people in unhappy relationships who post lovey dovey gushy stuff about their partner (usually around holidays or their birthdays) while simultaneously reaching out romantically to other people behind their partner's backs.
I also have a family member that is very happy and always posted photos of her and her husband, and would NOT STOP POSTING WEDDING pictures for like, a year after her wedding. My best friend was like, "Dude, I had to unfollow her." He is and also was in a happy relationship, so it wasn't because he was bitter.
So I think it's really hard to say. There is a broad reasoning for social media and human behavior.