You have to be able to talk about the A. I'm not saying a BS needs to throw it into the face of the WS every time there's an argument, but the more you talk about the A, the less it will surface DURING an argument that's unrelated. If there's even a remote possibility that your wife would reach out to a FOM just because you two had a fight, then SHE is not doing the work. She needs to find what she needs either from herself or from you. Other men are not an option in a healthy marriage.
How do I handle the fear that WH will talk to OW? I tell him I'm afraid. I give him the opportunity to hear me. One of the things I'm learning in MC is that it's not up to a spouse (WS or BS) to "fix" the other person's feelings, but it is up to them to acknowledge and validate them. It's normal to be afraid of ongoing contact between a WS and their AP. And it is the ongoing job of the WS to hear those fears, validate and reassure, and then do their best to continue to be transparent and prove that NC is ongoing.
Me: FWW (STA 2002), now a BW.
Him: FWH (OW1: 2006-2007), now just WH (OW2: 2010-2013)
I will never stop trying... because when you find 'the one' you never give up. (Cal Weaver)