It sounds like you're hoping for plausible deniability- which is understandable, you're devastated and don't want this to be true. But it sounds like you've got hard proof, so don't set yourself up to be taken for a fool.
How to approach it I think depends on what you want to get out of it - to hear the truth from him, warts and all? An apology? To try and reconcile? To watch him squirm? To prove you're right?
Depending on living situation and whether either of you can walk away you might consider the short sharp shock treatment - you leave while he's out, or you bag up his stuff and put it outside. Then say 'I know about Sharon, I have irrefutable proof. I want to hear it from you, so you tell me everything now and I might consider coming back / letting you back' (you obviously don't have to follow through with that).
Depending on what evidence you have, if what you're after is a full and frank confession to fill in the gaps for you, I wouldn't slap all the evidence down infront of him at first- I'd keep him guessing about what you actually have before showing your hand. 'I,e; I have hard proof of your affair with Sharon, this is your one chance to tell me your version of events'. I'd also print off anything you have - hard paper based evidence is more powerful than waving a phone screen around.
But if you just want to prove he's a liar before you walk away then by all means say 'I was being paranoid about Sharon was I?'- show him what you've got and then walk away.
Good luck, well done for outwitting this liar ❤️