Wait so at the end zenitsu didn’t end up with nezuko-

They did end up together. The girl that looked like Nezuko referred to Zenitsu as her Great (something) grandfather

There's a pair of siblings who look like zenitsu and nezuko, so zenitsu and nezuko are obviously married, so are tanjirou and kanao (since those kamado siblings look like kanao and tanjirou)

yeah I realized that after

Yupp I realized it after lol