I have to tell you from very recent personal experience that it depends alot on the two people. I never would've imagined that my husband would ever cheat on me. Then in November he started visiting different sex sites and relationship sites, some telling them that he was divorced and a couple he said he was married and looking for discrete sex on the side. This type of behavior was always something that he found repulsive in other men, looking at porn whether on the net or television he found disgusting... and yet here he was, now doing what he considered to be so lowly and trying to find other women outside of me. He began getting distant at home and acting not like himself.... and then slowly what was going on began to unravel... and it almost ended our marriage, because I didn't know what was going on or why he was acting that way. Then I found out what he was doing... and confronted him. While I expected that to be the end of our marriage... it wasn't.
He had violated trust, he had crossed lines that I never thought he would've of... and he was on the verge of meeting these women in person. As far as I know, he never did meet anyone face to face...
What happened though was that we both had to take a real long look at our relationship, our love, our bond... and I had to decide if I was able to trust him again, forgive him and allow us to move on.
I can tell you that our marriage is very strong, our bond is very strong... and that my love was strong enough to see us through a very ugly time. Will I ever forget what he did? Probably not. I don't know that it is really a question of whether or not I forgave him... or if forgiveness is really an issue at all, atleast for me. It has changed the way I look at him, and the way I handle life. Everyday I worry less and less because he is taking the steps to regain and rebuild trust.
Why did he stray... I don't really know for sure. Do I completely blame him? It takes two people to make a marriage work.
I can say that I am thankful that just when I was ready to walk away I didn't. I stayed... and we worked it out.. and we continue to work it out.
Do I monitor the computers? Hell yes I do... but that is more because I am a born skeptic and less because of him.
Cheating can ruin a marriage if their is no honesty. But before you end your relationship because your significant other cheated, think about your relationship... whether or not you really love them... then make a decision. No one is perfect, we all stumble and fall at some point... if the other person is willing to face what they did and try to make amends... give them a chance.