It's kind of hard to watch couples competing against, and not with, each other. I know the old adage of salary competition when both partners are working, but the competition can be about anything. Unfortunately, I have noticed that competitiveness nature more in men than women as one would guess. It also could be that, as a man, I am more in tune with how men behave and thus observe it more.
Nonetheless, I have a few friends that are couples and it's quite clear that they very much adore and love their partners, but at certain times, you get a glimpse of their competitiveness slipping. For example, I have a friend who has a knack for painting and is really good at it. Her husband, on the other hand, was never really interested in it. His interest eventually did peak and he picked up drawing. Now, I agree this all sound innocent and I sound like a cynical person but it's the change in interaction between them afterwards that drew my attention. You see, nowadays whenever I talk to my friend about her painting, she feels compelled to mention that her husband also paints. And the times when she forgets to mention it, you can see him visibly get sad/upset. Same thing I noticed between another friend, who is a professional singer, and her husband. There is this tendency to one-up their spouses. But they also really love their wives so those two things are not mutually exclusive.
The way I understand it is, no matter if you are married or not, you are subconsciously measuring and seeking new partners. So when your partner offers something that others find attractive, you run the fear of losing them. So you start advertising the same skill and try to undermine your partner's in hope to stay ahead in potential new match. That might also be one of the reasons you see mostly men, skillfully professing their love for their partners on social media with a dash of "marketing". A bit like advertising to potential women, "Hey, look at what you could've gotten" or trying to appear more desirable than those women's partners. I guess in the end, your intentions matter only so much if no action was taken and your partner didn't get hurt.