Just when it seems impossible to dredge up any more secrets about the life of John F. Kennedy, journalist David Pitts has written an eye-popping book called Jack and Lem, which details JFK’s intimate, 30-year friendship with a gay man.

Kirk LeMoyne (“Lem”) Billings met Jack when they were teenagers at Choate School for Boys in 1933. They were an odd couple, even then. In contrast to Jack –- Irish, Catholic, Democrat and new money –- Lem was establishment to his fingertips: Mayflower ancestors, Episcopalian, Republican and shabby genteel rather than rich.

Nevertheless, the two boys were drawn together by a shared contempt for authority and an unquenchable love of fun. From Choate to Dallas, the two spent every moment they could together. “Jack made a big difference in my life,” Lem would say in his later years. “Because of him, I was never lonely.”

Lem’s affection was reciprocated, despite the fact that Jack knew, almost from the beginning of their friendship, that Lem was gay.

Jack and Lem were inseparable within days of meeting each other, but Lem soon decided that being Jack’s boon companion wasn’t enough. In June of 1934, unable to contain his passion any longer, Lem wrote Jack a letter while Jack was in the hospital, recuperating from one of his frequent bouts of illness. The letter contained a sexual overture. Lem’s letter has not survived, but Pitts quotes Jack’s reply: “I’m not that kind of boy.” Incredibly, the two remained close despite the pain and embarrassment that this episode caused them both.

Even more incredibly, Jack not only involved Lem in all his election campaigns, from his first run for Congress in 1946 to his successful bid for the presidency in 1960, but kept him in almost constant attendance -- in Washington, Hyannis Port and Glen Ora, the Kennedy’s weekend retreat in Virginia. Jackie Kennedy, who liked Lem, sometimes found his omnipresence exasperating. She once complained that Lem Billings “has been a houseguest every weekend of my married life.”

Jack wanted Lem with him even though Lem had little aptitude for politics and could have proved a serious embarrassment had his sexual orientation ever become public.

Just how serious may be inferred from the arrest of Walter Jenkins, a top aide to Jack’s successor, Lyndon Johnson, during the climactic weeks of the presidential election of 1964. Jenkins was nabbed by the D.C. police for having public sex with a man at the local YMCA. Despite LBJ’s best efforts to kill the story, it made the papers and might have tipped the balance had the election been close. And Walter Jenkins did not have a guest bedroom reserved for him at the White House so he could come and go as he pleased. Lem Billings did.

Why did Jack insist on having Lem on hand, despite the obvious risk he posed? According to Gore Vidal, another gay member of the Kennedy circle, Lem was Jack’s “idiot friend” –- a court jester who amused him during his off hours, ran his errands and cleaned up his messes.

But there is ample evidence that there was more to Lem than that. A successful advertising executive, Lem was the inventor of “Fizzies” –- an instant sparkling drink that children could make by dropping an effervescent tablet into a glass of water. The tablet made an instant hit with the kids, and grew into a ten-million-dollar business during the 1950s and 60s.

Jack thought enough of Lem’s abilities that he offered to put him in charge of the newly-created Peace Corps. (Lem declined, and the post went to Jack’s brother-in-law Sargent Shriver.)

So what lay behind Jack’s attachment to Lem? David Pitts suggests that it was because Lem was practically the only person with whom Jack was completely at ease. Lem had known Jack since they were boys. He shared all of Jack’s secrets, and knew all of his faults. And he yet never judged him or gave him anything but unqualified love and unquestioning loyalty.

With Lem, Jack felt safe. With Lem, he could be a boy again –- joking, teasing and playing outlandish pranks.

Apparently, Jack reverted to adolescent horseplay for the much same reason that Lincoln and Reagan told funny stories –- to escape, if only for a moment, from the crushing burdens of the presidency.

Because Lem worshipped Jack, he didn’t mind being the butt of his hero’s jokes. This was just as well, since Jack’s humor could often be sharp-edged.

Pitts describes how Lem once returned from a visit to Europe, bubbling over with the news that he had become chummy with screen legend Greta Garbo. The two had actually toured the Italian Riviera by car together.

Lem’s bragging on his friendship with Garbo finally got under Jack’s skin, and he decided to get even. He invited both Garbo and Lem to an intimate dinner at the White House with just him and Jackie. But he arranged for the actress to arrive first, so he could enlist her in a little plot he had hatched to take his pal down a peg or two.

So when Lem arrived, feeling rather full of himself, Garbo pretended that she had never met him before. Abashed, Lem spent practically the whole dinner desperately trying to remind the actress of the times the two had spent together, only to have each effort met by a frosty denial from Garbo.

Finally, the three conspirators –- Jack, Jackie and Greta -– could contain their amusement no longer and burst out laughing. Lem was let in on the joke and, although shaken, he pulled himself together and managed to enjoy the rest of the party.

The date was November 13, 1963. Jack left for Dallas little more than a week later. After that night, Lem never saw his friend again.

Jack’s death devastated Lem. He lived on for another 18 years as a keeper of the Kennedy flame, transferring the tenacious loyalty he felt for Jack first to Jack’s brother, Bobby, and then to the Kennedy children. When he died in 1981, it was a cohort of young Kennedy men who carried his coffin to his final resting place.

An unnamed friend of Lem’s contributed an observation to David Pitts’ book that might well serve as an epitaph for this gentle, self-effacing but nonetheless remarkable man: “His closest friends were his heroes. To them, he gave everything he had to give.”