Ok... I have been on both sides of cheating many of times. I think it depends on the situation leading up to. I cheated on a guy multiple times many years back due to the fact some of his "friends" told me he was cheating on me... Fact was... his friends tried to hook up with me after our breakup... hmmmm... I fell for that one. A couple years ago when talking to this guy I asked him flat out about it... he cheated on me after I cheated on him the second time, he dumped me the third. To think things could have been different if we would have both been completely honest with one another... but things are for the best.
My husband had many an issues with fidelity... and shortly after we hooked up (within a month) was messaging a girl online telling her how much he loved her. After I found the messages... I confronted him with it... he claimed he was never going to meet her... and I shouldn't have checked (this was my computer at my house BTW) so I set up a fake profile and messaged him... needless to say... he asked me to meet him... and I did. After that big blow up he was good for about 5 years (as far as I know) then I noticed he was staying at work longer than usual, disappearing, even left me at a bar alone for over an hour. After some research I found out the blond girl from his work and him were flirting pretty bad, and he was locking himself in the bedroom to talk to her. After that time I really thought long and hard about leaving him, but I had grown to care about him too much. So we married. And I was faithful for the 7 years up to the marriage.
A little while after I got married my ex contacted me and we began talking, I told him about my life in whole (I did notice that my husband didn't like the fact I told my ex about the cheating problem). I noticed my ex would ask why I would put up with that, or that I deserved better. One night after some extreme all night drinking my ex made a move on me and we messed around. I had thought about coming clean to my husband the next day... but since I always figured things out on my own, I figured I could wait. After one month and another hookup I decided I needed to come clean to him. He was hurt, and I did feel bad... but all the times he stepped out of line... even if I caught him he always lied to me about it... to the point if I didn't figure it all out... he could still be lying.
I still love my husband with all my heart, and I still look at him like my bestfriend... but I felt so disrespected due to all the lying. Mine was a mistake made out of anger, hurt, and many other emotions. I'm not sure about his... I don't think he will ever tell me. What I have learned from the whole thing is that one act of betrayal leads to another... so it's best to have an honesty policy in place, so if I feel like hooking up with the ex again... I can, and he knows now that he could actually lose me, and it's not another empty threat.