I wanted to discuss with her about her treating me shitty last Friday when we were getting ready to leave for home from a vacation last week to her sisters house. We wanted to get out of there by 7 am and while I, my SIL and her husband were all up by 6 am, she didn’t get up until around 6:30. While her sister was cooking some eggs for breakfast, my wife yelled down the steps "Get your ass up here and pack your shit!" Her sister looked at me in disbelief while I yelled back "chill out".
If this is how she treats you in front of family, how does she treat you when it's just the two of you alone? I can only imagine. Is it common that she yells at you in such a disrespectful manner? You know your wife best and maybe she just woke up on the wrong side of the bed but is this a person you really want to fight for? A cheater that at times, in front of others, treats you like shit?
With that brief insight into your life (and admittedly, speculating and extrapolating into how bad it is for you at home) I am going to offer some further advice. While she may have taken some baby-steps to start looking into therapy, don't let up now. I would recommend continuing to detach from your WW. You previously posted that you have a flaw in that you don't stand up for yourself. Hopefully, you've realized by honestly telling your WW that you started browsing dating sites and that you should start the process of splitting up (i.e. standing up for yourself), has brought some results. Keep it up. See how she acts next week while being detached, no serious talks all week that are initiated by you.
Now, what I'm going to post next, may seem extreme and vindictive but you've been in hell for 3+ years... also I'm a big believer that unpredictability is the enemy of infidelity, while routine is an ally. You've probably been living your life in a "standard" routine for years... time to shake that up.
Depending on your calendar, on Thursday, tell your wife you're going out on Friday... and nothing else. Come home on Friday, clean up from work, get dressed up nice, but not too nice (don't wear a suit), put on some cologne and head out. Leave your phone at home on the kitchen counter and available for your wife to go through. If she starts asking questions, just say you're going out and she's free to look through your phone (there's nothing in the phone to find) and leave the house. You don't want your wife to follow you, to track you by your phone, or blow up your phone with calls/texts all night. You live in a small town so go to another town, or better yet, hopefully you live near a big city.. go there. Have sufficient cash on hand. Go out to eat at a new restaurant or maybe go see a movie you're interested in or hell, go bowling or a bookstore, whatever. Pay by cash so she can't track by bank account or credit card website. Keep the receipts to show you only bought 1 meal, 1 movie ticket etc... for later (maybe days later.) Take some time for yourself, and enjoy yourself.... and let your wife sit and stew. When you get back (hopefully around midnight or later) go straight to bed. Do not let her talk to you, if she insists tell her you've had 3 and half years to talk and she didn't want too, why start now? And nothing more, go to sleep.
The next day, if she still wants to talk (and I'd bet a month's salary that oh, she's going to be bouncing up and down wanting to talk) this is where you can use her exact phrase that has eaten at you for years.... just simply tell her that "whatever I did last night wasn't meant to hurt you (wife)" Let her feel how that phrase sounds like from the other side. Then get out of the house... go into work, go play 36 holes of golf, just get out for the day. If the hysterics start that night, or the following days... that's when you whip out the receipts and show your wife you were by yourself for the entire night. Tell her you wanted to experience what it would be like if you divorced and had to live on your own. Maybe throw in a remark "and it wasn't that bad."
It sounds like your son just got engaged... your WW needs a reality-check that you and her may be attending his wedding with different partners, if any. I'm sure your WW hasn't even thought that there would be a chance that she wouldn't be going to his wedding without you. She might need to start thinking about that.
While the above may seem extreme, childish, vindictive, manipulative and petty, it really isn't... you're taking a night off for yourself and that's it. You can't help what your wife is going to think. She's backed herself into this corner in her marriage. She needs to get herself out of it.