She keeps bringing up why I would think she would cheat on me, calling me insecure, badmouthing the potential OM, etc.
Hi HrtHsbnd, I'm confused. You said you believed she was cheating and gave arguments pro and con. Then you said you worried about treating her as a WW spouse and pushing her away if she's not. Then you "Let her know you know"?! How did you become certain? If you aren't, I can see how that might sound insecure. It's hard grappling with uncertainty. I've been meditating lately to avoid rash actions.