If you spend too much time trying to find out what is good or bad about someone else, you'll forget your own soul and end up exhausted and defeated by the energy you have wasted in judging others.
You can become blind by seeing each day as a similar one. Each day is a different one, each day brings a miracle of its own. It's just a matter of paying attention to this miracle.
I see is that there are many people who destroy their marriages because of one-night stands with someone else. And as the French say, "C'est ne pas grave." It's not something easy to swallow, but at the same time, it does not justify you to end a long-lasting relationship because something happened.