Tony, i think this site IS "for you" because you could learn a lot by reading around and learning from other people's mistakes (you can have credit for your own success though).
What you describe is not uncommon, this need to create artificial rules to "protect" your marriage.
In my world view, the only people who can threaten or end a relationship are the two people in it (ultimately, every relationship is one-to-one, even in an "equal triad" where all three people are involved with each other). If your relationship is solid, feelings for another person will not threaten it whatsoever. It's your spouse's behaviour and actions that will threaten it or not. I am going through this right now. I just met someone whom i am very into, i'm not going to get into the details here, but as wonderful as the new person is, as much as i can imagine what it would be like to start my life over with them, it does not change the fact that i was/am already happy and have no wish to leave the life i have now. The new person will have to fit in however they fit into it, and me into theirs.