Well, I can tell you about one case. He had a year-long affair with a woman named Mimi Alford (Tell-all book: Once Upon a Secret). It looks like he had handlers, basically, who helped find her and get her into his circle. In early 1961, when he first became president, Alford was a high school senior at Miss Porter's School, an exclusive prep school where Jackie Kennedy had gone as well. This kind of preppy girl, outwardly a lady, but dirty in the sheets, seemed to be JFK's "type". Anyway, at that time, Alford wrote to the White House in hopes of getting an interview with their school's famous alumna, Jackie, for the school paper. She was invited to the White House, where she didn't meet Jackie, but did meet Jackie's Social Secretary, Letitia Baldrige, also a Miss Porter's school grad, and she saw JFK for just a moment. The following year, out of the blue, she was offered a White House internship, which she took. Someone had chosen her--noted her from her first, innocent visit, and written her name down as a possible paramour for JFK. It's unclear who that would be. There were other women working on the staff who, it's rumored, had affairs with him, and they might have been enlisted for this purpose. But there are men, too, on his staff, who could have done it. In any case, as soon as she started the job, she was asked to take a swim (in a bathing suit the White House provided) in the White House pool, at the same time that JFK was known to swim there. The implication in her autobiography is that this was all set up by people who arranged his assignations. I guess she passed the bathing suit test, because by the 4th day of her working at the White House, an incident was arranged where she and JFK would be alone for a few moments, and he led her to the First Lady's bedroom (they had separate bedrooms) and he immediately started having sex with her. Their affair then continued until shortly before his death. In the meantime, staffers would arrange for her passage, for her to meet up with him, for her to travel on the press plane, to have a room, to get her alone with JFK, to get her to travel in cars with him and attend parties. Even to get an abortion should she need one (they never used birth control. At one point, she thought she was pregnant and she got a call about a doctor near her college that she could call to get an abortion. But the situation resolved and it wasn't necessary.) It looks like Special Assistant to the President Dave Powers was the main person that Mimi dealt with in these situations, so he might have been the main guy to make these arrangements.

Mimi was only there when Jackie was not around. Jackie often went with the kids to one of their other homes, so this was a fairly frequent occurrence. She went to parties with JFK where there were other women--it would have been easy for JFK to pick up other women in those situations. JFK also tried to "share" Mimi with other men, though I think she declined all such offers. People at these parties knew all about JFK, this wasn't a huge secret. In fact, the reason we know about Mimi Alford at all is because all the staffers knew about Mimi and were resentful of her, so complained about her in occasional memoirs, though didn't mention her by name. But they all saw her on the planes, in the hotels, and when she wore the same clothes 2 days in a row while working at the White House, they knew that it was because she'd spent the night with JFK. She got into the White House because she had an official job there, and when they were on the road and she got together with JFK, which was frequent, she traveled as Press. At one point she hid in a car, crouched down on the floor. After the Monica Lewinsky scandal, the idea that another president was sleeping with an intern became bigger news, leading to someone tracking down Mimi's identity, which is when she went public with it.