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.
One day you will wake up and there wont be any more time to do the things youve always wanted. Do it now. The simple things are also the most extraordinary things, and only the wise can see them.
About the nature of human beings. I discovered that confronted by temptation, we will always fall. Given the right circumstances, every human being on this earth would be willing to commit evil.