Are there any romances out there about "old marrieds"?

I'm waxing nostalgic on a Monday night and I sent a cute picture to my mom of my husband and my cat. And honestly guys not to brag, but I have a great relationship and a great husband. I got lucky. But it made me wonder- are there any good romances about great marriages? I'd love to read a book about a couple already in love? Does that go too far against the formula? Do they have to be on the rocks at first to make it a good book?

Just curious to see if anyone can think of something or if it's just too conflict-free for a good book. It doesn't have to be hetero or anything. Maybe it'd be outside of the traditional romance genre.