In my opinion, one of the most romantic married couples is Jason and Maggie Seaver! They met when they were teenagers, eloped, almost divorced, got back together, had four kids and their love and passion for each other was just as strong as when they first met.
People that watched the show honestly believed that Alan Thicke and Joanna Kerns were a couple in real life because of their amazing onscreen chemistry with each other. They weren't a couple in real life but had an incredible real life friendship that came across onscreen which made their characters so real. I've never seen a more believable and passionate couple than these two. They bickered and teased each other like married people do but adored each other and couldn't get enough of each other. The fact that they had been married for over a decade, and had four kids didn't even matter to them, they still loved each other deeply.
I think they are the perfect example of an ideal married couple. Everyone should follow their example. Was it any surprise that Maggie ended up having another baby at 40? ;)