The 'Falling Inn Love' actress - who dated the former 'America's Got Talent' host for almost three years until 2005 - spent a month reading her then-boyfriend's text messages because she was convinced he was being unfaithful but didn't want to confront him while she was working away.
And despite what her snooping unmasked, Christina began to see reading Nick's messages as ''entertainment'' while she was bored in her hotel room.
She admitted: ''One time I did, and I succeeded at it. When I was dating Nick Cannon, the password somehow worked on the first check, and I was right, and the next thing you know, I was reading. For like a month, I was reading messages.
''I was stuck in Romania. I had time. So I was like, 'I cannot bust him when I am away. I need to bust him in person, so in the meantime, I'm gonna get my intel, make sure that this is for real for real, and it was for real, so it was enough.''
''I couldn't help it. I was bored, too, so it gave me something to do,'' she admitted. ''It became like entertainment.''
The 37-year-old star admitted she had a hard time coming to terms with losing her ''first love''.
She added to E! News: ''We were just so close that I think at that time, I couldn't deal with the idea that if we ended up breaking up, I wasn't going to get to see him again.
''So I wanted to be able to see him in person, go over it -- not like it would change anything -- but part of me was like, he was kind of like my first love at that time.
''It was unreal that it was happening. He was living at my house, everything. It was just like, 'Wait, under my roof this is happening?' It just kind of blew me away.''
Christina - who has nine-year-old daughter Violet with The-Dream and is expecting a baby boy with boyfriend Matt Pokora - now sees her split from Nick as a blessing in disguise.
She said: ''When I look at it now, I'm like -- I mean, not that it's right because I don't think it's right for anybody because I was doing good -- but, you know, it is what it is. And obviously, it wasn't meant to be.
''And I'm sure he's maybe changed his ways. I'm sure. We all grow up.''
Nick has previously apologised to Christina for his behaviour during their relationship.
He said in 2012: ''If I didn't say it before, I do apologise. I'm sorry for the things that I did. We was young. I was young. I was silly.''
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