Last I checked, you don't need Viagra for "kissing," so it's probably just best to assume it's gone beyond that and deal with this all at once emotionally. Cheating spouses will usually cop to one level LESS than what they are really doing.
Do you have any friends or family you can get with today nearby? Or a priest or minister or someone who can counsel you? Today is going to be rough on you, and you're going to need some calm, levelheaded support.