"I just feel that if while we are trying to work on our marriage these next four weeks, I find it hard for myself to see other people (she thinks we are both seeing people) while I want to focus on our marriage...what are your thoughts W?"
I think that's the acid test, Vince. Is she agrees, then you oughtta see her sincerely giving up the OM and working on the marriage. If she disagrees, well, that's your cue.
Excellently worded, BTW. Not issued as an ultimatum, and giving her a choice without pressure.
One thing though. You say she suspects that you may be seeing someone. Might she think this is your way of corralling her while misrepresenting your intention to not be involved with others? If so, she'd need to be assured that you're not seeing someone else.