Sorry you are here. There's a lot in your post to chew on and I'm no vet, but here are some thoughts/questions:
1. "It just felt like there was this imaginary wall that kept us from really moving further together" So it sounds like you guys didn't discuss the big things in life and you didn't argue well...so to keep the peace, you avoided conflict?
2. "It got to be the middle of November 2016 and I could sense a change in her attitude. I had to ask repeatedly before she finally admitted that she was feeling depressed. She said she didn’t want to wake up and be 40 and have not had kids or travelled. That she had nothing to look forward to. She asked me if I had goals in life, things I wanted. I struggled to find the words and the courage to say them before she gave up." These are typical mid-life questions (not necessarily MLC)...the fact that she was asking you is a good sign (but probably just the tip of the iceberg in terms of her true questions/thoughts feelings)...why did you struggle to answer them? She was trying to emotionally connect with you...and it didn't work.
3. "Still, I started to treat her extra nice and give lots of encouragement and affection. She responded well to it. Things felt like they were moving in the right direction." Not sure if you have read the 5LL book, but it sounds like you were trying to connect with her through acts of service...and she is trying to connect with you through quantity and quality time/conversation...
4. "Over the course of the following week her attitude took a nosedive. On Friday 12/9 she came home from her 3rd after work happy hour and barely said a word." It sounds like you think something happened at the work party? OM/EA/PA?
5. "So I had to ask repeatedly what was wrong before she finally let loose on 4 hours of tearing me down in every way possible." This dump sounds like my W...which happens when a person bottles up their negative feelings for years in the hope of avoiding conflict in the R (see #1 above).
6. "I said I could be better and that we just need to improve our communication." Sorry, this is way more than just about communication...but think you know that...
7. "I said how I wanted kids and I wanted to travel more." Bingo! You started opening up about the big things in life, what you want, what you envisioned, this is what she was asking you about before (see #2).
8. "She said she wasn’t sure she even wanted any of those things with me anymore. We finished talking and she went to the grocery store, where she still purchased items for me." So when she wanted to discuss...you couldn't...and now you are opening up...and she is closing up?
9. "We talked a bit more the next day but it was more of the same. At one point I was trying to get her to come over to me while we were talking because she was walking around doing various things. She said, “No, you’re just going to try to hug me.”" What's the dynamic in your physical/sexual relationship? Are you touchy? Is she?
10. "I asked something I never thought I’d have to ask: if she was seeing someone else." Sorry, dude. So many of us here have had these conversations with our spouses, but every one is heartbreaking.
11. "She got a sorrowful look on her face and came over and hugged me while saying “I don’t mean to hurt you.” I left to go to work." Okay, she doesn't mean it...but she's going to anyway?
12. "Told me she didn’t miss me, that she didn’t think she ever did in the past on work trips. That she just missed her bed and the dog. I know that isn’t true." This is called rewriting history.
13. "I told her I need to tell her how I felt and pasted in a letter I had written the previous 2 days." Sorry about your letter/confession (think most of us here have tried some version of them)...but with the OM in her head and heart...she can't respond to you...
14. "It turns out this was BS because I found out she was telling friends how happy she was I was gone and enjoying her freedom." Sadly, lying comes so easily...
15. "I calmly told her I wasn’t leaving, that if she decided she didn’t want to be with me, she could leave." Good for you!
16. "She said she didn’t have anywhere to go so if I stayed I wasn’t going to like it. That she wasn’t going to speak to me, buy anything for me, or tell me where she was going or who she was with. I didn’t know who this person was." Sorry, this is not the woman you married.
17. "I did kick her out of the MBR and into the guest bedroom, which she was irate over. I told her that was our marital bed and if she didn’t want to be married then she could sleep elsewhere." Again, good for you!
18. "We didn’t speak much, the tension was very thick. It was during this time I started to analyze and investigate more. I was able to find out who the OM was." I have previously noted that the affair partners are quite a cast of characters...but a married with kids, drug/alcohol addict who tried to shoot himself...wow, what a catch!
19. "I would try talking to her at times over the next week. She was cold but maintained she didn’t want to file for divorce." Do not initiate R talks.
20. "Christmas was spent apart with our respective families. I’d gathered by then that she was telling her family and friends that she was abused and painting me as an awful person." Yes, perhaps some lies and blameshifting...but you also have to take ownership for your own contribution to the failed M...
21. "On 12/29 I came home from work and initiated a serious discussion. She finally seemed a little open, a little empathetic." Their moods swing wildly...from hot...to cold..try not to read too much into these swings.
22. "Eventually, I went to the MBR to go to bed. Something urged me to check her nightstand, where we kept condoms. I opened the drawer and 2 boxes and a vibrator were missing." Doesn't sound like you were confused...but in denial...
23. ""So I said, “2 boxes of condoms should keep you gone longer than that.” No reply." LOL
Gotta run...but will complete later...
Gordie 40s W 40s M20+ kids 2016 BD W fantasy affair w OM1 I do everything wrong 2017 I start to DB W says TLTL files for D PA w OM2 2018 I do LRT W drops filing and OM2 situation slowly improving