He didn't have an affair with Marylin Monroe. His brother Bobby is rumored to have. Monroe was invited to his birthday party once and sang a very provocative rendition of 'Happy Birthday'.
During the 1950s American had the feeling that we were locked in the Cold War, that nothing big was happening. Eisenhower was a much-loved president, in fact he was so popular at the end of WWII that both parties wanted to run him for president. But Eisenhower was a 'do nothing' president at the time we needed a do-nothing president. We were in an unprecedented wave of prosperity after WWII and Eisenhower used that money for a lot of good things--a national highway system, the polio vaccine (and other vaccines) that saved thousands of lives, stuff we needed. But people still wanted the country to move ahead.
JFK was relatively young and good-looking. He spoke well, which is important for a president. His whole campaign was that we had stagnated and we must move the country ahead with vigor. The media loved him and portrayed him in a very positive light. I knew a few people in those days who said 'He's not MY president', but in general the country was much more united in those days than now.
If you can relate to Obama better, it's because Obama is more a president for the 21st century. JFK was his equal, but in a different time, a different set of circumstances.
Also getting shot was a 'good career move'. A lot of people are more famous after they're dead--Elvis Presley, Martin Luther King, etc. His shooting was an enormous shock for the whole nation. It was almost unimaginable to think that an American president could just get shot like that in a parade. If Obama had been shot, or Trump, a lot of people would say 'Well I hated the guy anyway, so good. He had it coming!' But this is today's world, the world you grew up in, where all presidents are hated by about half of America. When Kennedy was shot you didn't hear that (much). It was more like 'Oh my God, how could this happen?'