This isn't about me - but I am the only person I can speak about, so here goes:
A thought: If you found out that the only girl you were with was providing someone else to ride the skinboat to tuna-town, how would you react? If for no other reason than potential STD exposure, I would be enraged. It might also call into question my feelings of my value and whether "everything" had been a lie.
Forget what she thinks of you. In my marriage, I try to tell my wife the truth (with respect); I should be accountable. Knowing that may actually help keep me from doing things I wouldn't want others to know about. Also, I respect my wife enough that I would prefer that she was honestly PO'd with me, rather than dishonestly pleased with me.
I'm not "Doctor Phil", but this seems to be hitting your concious. It is your call, but if the roles were reversed - how would you feel about her playing spin the cooter without your knowledge?
All that said, I can certainly see the reason you would want to maintain the status quo; the real question is - at what expense?