My arrangement with my husband is that I can doing anything (physical) with anyone I want, and I have no interest in any kind of emotional anything with anyone but my husband.
That said, "cheating" doesn't really exist for us, and I know he would be excited if I were doing stuff without his knowledge. Here is the thing tho, in general I don't have a lot of free time, and so stuff usually happens at our apartment. And if I meet someone I don't already know or trust, I want my husband there for safety and such.
With all that in mind, if the opportunity came up, I'd hookup with the right person and wait a while before telling my lil hubby