The 26-year-old model tied the knot with the 86-year-old Playboy founder last New Year`s Eve (31.12.13) and she admits her constant worries that she would be "replaced" by another girlfriend led to them agreeing to wed.
Asked why they had married, she told `Huffington Post Live`: "Well for me it meant more security, knowing that I am the one for him.
"Like we were talking about, there are always girls in and out and always the feeling of maybe being replaced ... And he made sure I didn`t feel that way anymore and that was what the wedding was all about."
Crystal - who originally called off her wedding to the media mogul in June 2011, just five days before they were due to wed - says she fell for her new husband because he is so "intriguing" and they share a passion for psychology.
She said: "When I first met him, I had never even met a celebrity in my life before. I was like, `Oh my gosh Hef,` and then we started talking.
"And we both studied psychology in school. He`s very intriguing, I`ll ask him a million questions. I`ll ask him everything and we`ll watch all of his documentaries and he loves revisiting all of that stuff.
"And I love learning about all the history ... Just being more involved in his life and learning about Playboy and all the things he has done to change the world."
Crystal - who is the father-of-four`s third wife - says the build up to their first wedding was a "big ordeal".
She said: "Last time it turned into a big ordeal and then it all fell apart."