My boyfriend and I have a semi-fictitious "List" of guys we are allowed to partake in.
The part that is real are the celebrities on the list. We both have an understanding that if one of us is presented with an opportunity to fuck a celebrity, we should probably take it up. We also agreed, though, that we should do our best to include the other, or film it/take pictures (if possible). We also agreed that we should let the other know beforehand, just in case the other had an issue with it.
The part that is only sort of real are the guys that we will pass on the street, or friends of each others' that are really hot. In those instances, they must be 3-ways.
We both had a sort of cynical talk about how almost all relationships result in either infidelity or bringing a 3rd (or 4th :wink: ) person into the bed. We agreed that if we get to that point to include the other, rather than do it behind the back.
Although we also, upon later discussion, decided that neither of us were comfortable with the other doing anything with anyone else in any situation other than together (or with the celebrities).
But to answer the question from my standpoint, I will not do anything dishonest, and I will not do anything that will jeopardize my relationship with him. He's the best I could ever hope for, and keeping him in my life is more important than finding someone else to have sex with.