I have mixed feelings on polygraph testing, but many have gotten "parking lot confessions." A WS will agree to a polygraph likely hoping the BS won't go through with it, then get as far as the parking lot of the polygraph place and spill their guts there.
For me personally it was a money thing, and my wife spilled a lot. She was pretty damned candid about it. I was able to corroborate most of her story by reading her messages with 2 of her (now ex) friends. She blabbed a lot about it with them. It all lined up.
Gr8ful referred to my story. What happened was my wife was less than forthcoming at first. She jerked me around for about a month by withholding info and insisting on remaining "just friends" with her AP. She flat out lied to my face about a couple of things. This was before I discovered this site. I eventually got into her tablet, which is synced with her phone, and saw some heartbreaking messages between her and a couple of her friends. I knew she was lying to me about a few things. I hit my limit. I started calling divorce lawyers and real estate agents right in front of her and set up some consultations. When she realized I was serious she broke down, spilled everything and begged me not to go through with it. That was about 14 months ago. She's been a model for reconciliation ever since. We're still together.
The point is, sometimes it takes some drastic steps and measures to get a WS to realize just how devastating their affair is to the marriage, the BS, and get the whole truth. You're off to a different start than I was in that she voluntarily confessed to you and I had to do a little bit of detective work and leg work to find out what was happening. My wife wasn't planning on telling me anytime soon.
If you suspect she isn't being honest with you and you go that route you don't want it to be an empty threat. You have to really mean it, so don't do it half heartedly. I was dead serious. As much as I didn't want a divorce I decided that there were worse things, and living in uncertainty and infidelity was one of them. As long as she's in contact with the AP, even "just friends" (there's no such thing once that line has been crossed) then the affair was still ongoing and under no circumstances was I willing to share my wife. If you backpedal or don't follow through without the truth you'll actually lose respect and she might walk all over you.
Now, we don't know your wife. Maybe she'll be one of those rare examples who fully "gets it" early on and tells you the whole truth. It happens. Rarely, but it happens. I think her coming to you and confessing is a good start, so there's that. Combined experience here tells us that most hold a lot back at first tho.
What you don't want is for her to run the show. You heal on your terms and at your pace. This is likely going to be one of the hardest things you'll ever experience. I'm 56 years old and it's probably the worst thing I've ever gone through. I didn't realize how painful and destructive affairs were until it landed in my lap.
Take your time in making any permanent decisions. Like we've been saying, you'll likely be on an emotional roller coaster for quite a while. How you feel now might completely change a half hour from now. It's a rough ride. I hope your wife is strapped in and up for the task if you decide to reconcile. Like I said, the timeline is typically 2 to 5 years for recovery. Don't rush things and don't try to sweep this under the rug. It will come back and bite you down the road. Sometimes years later. We've seen a few posts with titles like "spouse cheated ten (or even 20) years ago and it's killing me."
Either way hang in there. It does get better. It might take 2 to 5 years, but it does improve over that time period. I'm not "over it" at 15 months, but I'm (we're) in a much better place now. There are many aspects of our marriage that are vastly improved and we talk about everything now. In many ways we're closer now than we've ever been, but it came with a lot of conversations, work, some therapy, and patience on both of our parts.
