Was'nt there a book written about what he got up to with boys in India?
Could be. In about 1972, we had a geography teacher who had served in India at the end of WWII. He'd been a captain in one of the Punjabi regiments and had just arrived in Delhi from Calcutta to be briefed on his next posting, which was Saigon (that's another tale, but British and Indian troops were deployed to Indo China. Their numbers were such that they couldn't police the populace so, on orders from London, they re-armed Japanese POWs and let them loose again).
Anyway, according to Captain W. (he's still alive, aged 92) it was fairly common knowledge at G.H.Q. in New Delhi, that Mountbatten's wife was seeking comfort away from the marital bed with none other than Nehru. Mountbatten wasn't too bothered as he was quite fond of his houseboys. He was allegedly fond of entertaining young naval ratings too, but that may have been later on in his career.
I don't think I've read or heard of a book about Mountbatten's preferences, except for a mention in a book about Tom Driberg who unequivocally stated that he was a homosexual or at best, bisexual.