I have no experience with finding out about my parents cheating, but sadly I don't think I'd be completely suprised if I found out one of them has.
The only experience I have with being cheated on, and to what extent I will never know, was with my first ex. A while after we had been dating he tells me that he made out with one of his ex boyfriends when he and I first started dating. Being the asshole he is, he told me it didn't matter that he cheated on me because we had barely started dating and that he chose me not the other guy. Guilting a teenager into that sort of thing is not a very nice thing to do. heh....Of course, my fault for being with someone a bit older than me. But, when I found out I was really upset. And of course he cybered with men and had little shows on his webcam. So, I really had no idea what to think, but I was an idiot and he told me he loved me, so I stayed, but I never really think twice about it. That ended and I'm onto better things.
I'm not the brightest person when it comes to relationships. I tend to leap in heart first, so though I am young, I end up falling in love, or thinking I have anyway. I've learned that trust is really important from my experiences with my exes. The only thing you can do is trust in your signifigant other and hope that they trust you too. I can't doubt people for the rest of my life because of one asshole boyfriend. If it happens to me again, its just life and I'll get over it. Just always remember your own values and don't let others sway you.