A relationship must have absolute trust as one of its founding stones, that is something that most everyone would agree on. What trust means, what it entails, differs from couple to couple.
For example, I know a 'married' couple (I put married in quotations, because they were married using a pagan ceremony that isnt recognized as official) who are open to having multiple partners throughout their lives. In fact, the bride composed and sang a song to her groom about her blessing and accepting any future partners he would find. Every other couple has its own distinctions as to what is cheating, and what is acceptable.
I remember having this discussion with a bunch of girlfriends awhile back. It was the general consensus that touching was forbidden, but looking and talk/flirt was accepted. Because, and I quote, everybody does it.
You see, all this reflexion was brought upon by two people in my training class that I sit next to, and so hear everything they say. They are very obviously flirting with their words, their eyes, and their eyes, without ever touching. Which is fine, except for the fact that one of them is engaged. Now, far be it from me that I would ever express my discomfort with the way they act. I would never just saunter up to her, and say Hey! Is that attitude really appropriate for a soon to be married person? Or to him and say Hey! Would you be cool if some guy tried to woo your girlfriend knowing full well she was taken?
So I keep all my judgments to myself, and try to squash them, because really, who am I to judge you?
But at the same time, this has brought upon me a realization that my definition of <cheating> has changed. I now define cheating as anything I wouldnt do in front of J with a member of either sex. Words, glances, anything that I wouldnt do with J sitting right next to me, is something that has become innapropriate for me to do with anyone. Because, really, if I cant do it with him being right there, why would I do it at all? And vice versa of course.
The most important relationship in my life, apart from the one I have with God, is the one with my husband. It is up to me to keep the vows I said when I was married in every sense of the term, and never do anything that would break the sanctity of those vows. That doesnt mean never doing anything J doesnt want me to (were both extremely stubborn) but it means making sure I am the most trustworthy wife I could ever be, with my thoughts and actions and words.
Just another little nudge from God, I suppose. :)