You're the best polygraph. If your gut is telling you something isn't right, listen to it. Chances are she's downplaying the event, and there is probably more to it than you think.
Since she's lied to you, your trust has been broken and it's up to her to repair it, especially since this concerns an EX. They don't hang around for 'coffee', that's bs. Ask her to see her cell phone bills and/or email going back to a specific time period.
You have to ask yourself a couple of questions; why would she disrespect your relationship by involving an EX in the picture? And she disrespected you personally. Relationship are difficult enough without bring this junk into the picture. It's like putting a square block in a round hole.
