Hello OP:
Sorry you've joined the club nobody wants to join. First order of business is to take care of yourself. Hydrate. Exercise. Stay off the sauce.
Second order is to read in the "Healing Library" on this site. There is a lot of good info for newly minted BH's.
Third, no sex with the wife until you have both taken and gotten clean results from STD tests. Seriously. Your health is at risk.
This is pretty much the crux of what every new BH faces:
the woman I thought I knew wouldn't have had sex with a married stranger even when she was single.
What we all must come to grips with is that the actual, real-life, flesh-and-blood woman we are married to is not the woman we thought we knew. The bride we thought we were married to, that is an imaginary person who does not exist in real life. Though it's wise to not do anything too rash, the main thing that you must come to grips with is an honest, clear-eyed assessment of the actual woman you are married to. Clearly she is deeply flawed as a human given the course of lying and cheating you already know about (more on that below). Your marriage cannot survive, among other things, unless and until she herself realizes that and takes steps to fix it, to make herself into somebody new, and then in turn you decide if that somebody new is a person you'd like to be married to.
Which leads me to this:
And I'm not convinced I've heard the entire truth.
There is no way for us to opine on this question based on the short summary of your post. However, Trickle Truth ("TT" here) is very common among WW's when first discovered. Way more common than not, and it is normally a component of minimizing, also ubiquitous among newly outed WW's. The probability is high that you have uncovered the tip of an iceberg, but that is merely surmise at this juncture.
I will tell you that a saying here is "trust your gut." Your gut is telling you there is more. This is a strong indicator that there is more.
However, even as to what you know, the number of times she had to look you in the face and lie to you, either outright or by omission, over the past 5 or so years is quite large. An consider the ways she has taken from you that are in addition to the usual abuse associated with infidelity: exposing you unwittingly to STD's, which is a higher risk than in many instances since at least some of her cheating was via trolling casual sex web sites; spending family money on hotels, lingerie, etc.; leaving her 2-year old son for sex with another man (what mother does that?). Clearly there is something profoundly fucked up in her moral compass.
I do feel a need to point out one thing. You say:
Well back in July 2021 when she first slept with AP1 it wasn't good. We'd just moved into a new house, she hated her job (hence the move) and that combined with the every day stresses and strains of looking after a young child meant that we totally disconnected with each other. We blamed each other for every little thing that went wrong and I'm not even sure we could even say we were friends at some points.
If you read here enough, you'll see that your view of the causes and reasons for the strain in your marriage is wrong. This fact pattern outlines a classic description of the kind of abuse a cheating wife heaps on an unwitting betrayed husband. Picking fights. Finding fault. Making him feel like he is the cause of the marital problems. My friend, it's a classic case of gaslighting, creating a smoke screen of confusion that enabled her to carry on her cheating. Once you begin to see the truth of this, your anger will likely set in. That' a natural part of your progression through the shit sandwich your WW has been feeding you.
I wish you well. I will point out that if you've been married 5 years, with a 2-year old son, you're likely a young man. Maybe mid-30's, or possibly 41 if, as your name suggests, you were born in 1981. Still plenty of time to start over. Consider what the Shaker81 you will be staring down in the bathroom mirror in the morning 5 years from now, or 10 years, will say to you about your decision today.
By the way, depending on the state you live in, the fact that your wife left your son home with you for the purpose of sex with another man, that could support an award of primary custody to you. This leads to my final piece of advice. Find a decent family lawyer and pay for an hour of his/her time for a thorough consultation. The cost will be about the same as the amount she spent on lingerie and hotel for sex with another man.
I'm NOT suggesting that you file for divorce. Rather, I'm advising you to learn from a lawyer exactly what a divorce would mean for you in terms of finances, custody, etc. You can't choose R unless you know what D entails. Be sure to ask if your state offers "for-cause" divorces, which could get you out of any spousal support. And also ask about the possibility of you getting primary custody based on the facts recited above.
[This message edited by Butforthegrace at 5:13 PM, Tuesday, March 8th]