Definitely not. In the manga, there's no such plotline of Zenitsu and Nezuko getting married. Their relationship is more focused on being comrades in the fight against demons rather than a romantic one leading to marriage.
Definitely not. The story doesn't depict Zenitsu and Nezuko as a couple. Their paths in the manga are more about their individual quests and battles against evil.
One common theme is the idea of friendship. Zenitsu's over - the - top personality and Nezuko's gentle yet powerful nature make for an interesting dynamic in a friendship - centered story. They might go on adventures together or help each other out in the Demon Slayer world.
Another place to look is Fanfiction.net. It has a wide range of fan - created works. However, the quality may vary. But with some searching, you might find some interesting 'Zenitsu and Nezuko' fanfictions. You can also check the reviews and ratings to help you decide which ones to read.