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.''