Found some friends who are going camping for the weekend. Think I'll stay overnight with them and then show up in the morning.
Good deal. I'm impressed by your jump-into-action, Kieran. Much kudos to you, sir.
Now, this is IMPORTANT. When you get back tomorrow morning, do NOT brood! Don't be p*ssy, don't be pouty, don't be petulant, don't even be MAD. (SHE may be livid, but you'll have your spew jacket on, so don't let that rattle you).
Your demeanor and your words should be: "This isn't what I wanted, but I realize now that whatever happens, I'll be okay. I realize now that I deserve someone in my life who is 100% committed to me, and who is truthful with me and faithful to me. I still hope that that ends up being you, but right now I'm not sure how I feel about that anymore. A lot of trust has been broken here."
and
I AM FINE; NOT THRILLED, BUT HEY -- I'LL BE OKAY AND I KNOW YOU WILL TOO.
If she says "Are you mad?" say "I'm not mad, I'm just deeply disappointed." Nothing more.
If she asks "What are you going to do?" or "What are you thinking?" say "I'm not sure yet. I still have some other people whom I trust to talk to, and some decisions to make, as I'm sure you do too."
If she starts SCREAMING at you, like "WHERE THE F*%$ WERE YOU?!" and "WHY DIDN'T YOU CALL ME, I WAS WORRIED SICK!" say "I'm sorry you were worried; I'm fine. I just had some thinking to do . . . and still do."
If she starts with "This is why I could never stay married to you," or any other kind of spew, just say "I'm sorry you feel that way. I understand. I'm just trying to do what's best for me right now." (or similar)
If she promises you she's ended her affair, she's told OM it's over, she wants to work on the marriage, etc. ....
Say "Yes, I heard you when you said that yesterday, but when I told you it wasn't that easy anymore your response proved you weren't sincere. If and when you're really committed to what that will look like, we can discuss what it takes. I'm too tired to have that discussion right now though." (and again, ALL of these are delivered with a smooth tone -- no anger, just courteous). Or you can also say "I wish I could believe you; I've got over two years of deceit I'm going to have to process first. We can talk more later."
You can EVEN say (so long as she's not spewing at you), "Look -- this isn't what I wanted. I do love you. But obviously a LOT of trust has taken a huge hit here. Frankly I don't have any answers for you right now, and it's CERTAINLY not my job to make YOU feel better about what's happened today, so if you'll excuse me I have a couple of errands I need to run" (or "I need to grab a shower," or whatever).
The only other thing I'd add is that if she is downright RUDE or DISRESPECTFUL or SCREAMS at you (including whatever amount of profanity or obscenity you might ordinarily put up with), just put your hand up and say "If you're going to talk to me that way, this conversation is over. When you're ready to calm down and discuss this respectfully, let me know. I'm going to grab a shower" (or whatever)