Jawahar Lal Nehru never wanted to marry and the Mountbattens had an open marriage i.e. they could go out with or date anyone they wanted without asking each other.
Edwina’s and Nehru’s respective troubled marriages brought them close to each other.
I’m going to add text from original letters written amongst these people that will explain things better. To understand what they had between them it is important to understand that none of them was happy with their marriage. Let’s go one by one:
Jawahar Lal & Kamala Nehru
He was sent to Trinity College, Cambridge, England at the age of 17 where he read a lot and became good at things. He made lots of friends from around the world and was influenced by British & western thoughts and learnt to think freely. It soon became clear that his thought were different from his father and that was ok until it came to his marriage.
It was in 1909 that Motilal Nehru wrote in one of his letters about his opinion about getting married to which Jawahar replied “I’m not violently looking forward to the prospect of getting married to anybody.” Although he was in general against marriage he also in a way made it clear that his enthusiasm would be higher to the idea if the girl would be from outside the Kashmiri Brahmin family.