In which Nancy Drew books are Ned and broken up?

Ned and Nancy never actually break up in the original Nancy Drew series. They have a few disagreements and misunderstandings throughout the series, but their relationship is largely consistent.

Their relationship is more implied than explicitly detailed, as the focus of the series is Nancy's detective work. While there's a sense of romantic tension between them, their relationship is largely platonic, emphasizing their friendship and shared adventures.

It's worth noting that the relationship dynamics between Nancy and Ned have been explored and reinterpreted in various adaptations and reboots of the series.