I love dramas / movies about marriage, but most kdramas and movies around this theme are very depressing. It's always about cheating and how much the spouses hate each other. Ugh ... who wants to spend hours watching that?
If you want to watch dramas where the marriage isn't always acrimonious (which is not to say the couple doesn't face challenges, but they continue to love and fight for each other, instead of against each other), try Golden Bride and All About My Mom.
Golden Bride is very draggy in parts, but somehow I managed to finish it and rated it an 8 because the leads were so good to each other, despite all the challenges marriage brings.
All About My Mom is not a drama about marriage in and of itself. It's about how important mothers are in spite of the fact that children and spouses often take them for granted. With that said, there's a young married couple in the drama that I feel is totally worth watching. They go through their ups and downs, but they never turn against each other.
Both are long 50+ dramas. I will understand if the length deter you, but both are worth the watch, imo.