Your poll doesn't make sense to me. If you'd slept with this other woman, then for me, I would tick 'leave'. But it sounds like you are flirting, not having an affair.

What do you want to do now? Why should it be your wife who makes all the decisions on leaving or staying? Are you willing to give up 20 years of marriage for a what could be a daydream? Do you really love your wife? Why did you start up something with an old friend? For me, those are more important questions to ask, rather than if your wife should stay or go.