Best answer that sums it up.
Right on americanpie3. Even when you meet THE one, as henry007 says, there is no single human being, as perfect as she is, that can fulfill all of your needs. For e.g you may have a passion for classical music or dark metal, and she hates it!! You can go on for a while without it, if it is really the only thing that she's not sharing with you, but at some point you'll need your shot.... Also, after a few years, boredom sets in, like it or not. So, what do you do? You break-up because you have a devouring fantasy you need to appease, or you do it discretely and go on? You get some excitement that spices up your couple life? What is the least damaging thing to do? Not sure...
I hear all the idealistic arguments of the self-righteous: "Didn't you promise her to be faithful", "What if she did this to you", "If you don't love her, you should have the courage to leave her" and the like. This works when you're 20 years old and naive, and these are the hooks that women use to own you. However, on my side when I had a steady long-term relationship, I never promised to be faithful. We never discussed it and some would say it goes without saying, it is the norm. But we never did discussed it. And even if we had, on to the second point: What if she did this to you? Well, those of you who have been living in couple for a long time will understand this: after a while, physical faithfulness is less important than relationship. I would feel more offended if she fell in love and preferred another man, but if she had a one night stand, I genuinely hope she had fun!!! And if this makes her kinky and hot in my bed, all the better! And about the courage, that one is a bit less black and white. If you hobby because you're miserable and lack courage, that is one thing. But on the other side, it is my experience that hobby feeds your fantasies, increases your libido and actually keeps you from breaking everything apart because of a one night itching fantasy you need to appease (for e.g. a duo, or anal, or CIM or some other thing she won't do). And in the end she benefits from that also!
Now if you've never been in a long-term relationship, or for long enough (I'm talking 8-10 years and beyond), this may be difficult to grasp. But I am of the opinion that hobby does keep couples together and prevent sex crimes by providing an outlet, and not the other way around.
