Okay, big update! Spoiler alert: every response to this thread from now on is going to be "I told you so."
So. Earlier today, I got an email from the other guy. It was a weird test email with no real content. I later found out that my girlfriend had BCCed him on her breakup email to me, and he responded to it because he wasn't sure if she had even sent it to a real email address. So A) he's not the sharpest tool in the shed, B) the lack of trust is starting even earlier than usual with these two, and C) it was immediately obvious that she had been in contact with him beforehand.
She still wants to get back together. Tonight, I called her and I told her that I knew she had contacted him. At first she denied it. Then there was a long silence (like 2 full minutes), and then she admitted to talking to him, and then she admitted to meeting up with him. I asked her about sex, and she said "not every time". So hey, not so bad right?
We ended up talking for about an hour. I was resolute in saying that I was not willing to try again, especially after this. She told me that she had been confused and felt like she needed to figure out what she wanted (again? I thought that's what happened the first time around?). She also said that she had fully intended to stay true to me, but after I sent her a particularly angry email, she had lost her resolve and turned to the other guy for comfort. I looked at the timeline, and that means that she lasted almost a full week before cheating on me again! And she's been seeing him for about ten days. I don't doubt that she was going through tough times, but I can imagine more constructive ways of getting through them.
She told me that she really really really meant what she said earlier: that after she sent me the breakup email, she immediately realized that she wanted me, and that she's totally 110% sure this time. She asked me over and over again if there was anything she could do to change my mind. It sounded like she would have quit her job and hopped on a plane right away if I had asked her, which was a little bit gratifying. And I won't deny that a part of me wanted to accept her adoration and passion. There's a lot that I'm going to miss about our old relationship. But I told her that no, I was not going to reconsider, there was nothing she could do, and that we should both move on.
I'm sure she'll go back to the other guy now. Although I bet this complicates their relationship; at one point he had told her that he really didn't want to be her "second choice".
After that call, I wrote again to my parents and my brother and some close friends. A few minutes later (as I was writing this post, actually) she called again, but I let it go to voice mail three times. She texted me "please talk to me". I said no. She told me that we can still make a different choice. I told her "I'm not going to reconsider. I'm going to put my phone in airplane mode now." And I did.
So there you have it! You guys were right all along. And I was so annoyed with you for insisting that this would happen! I apologize. I'm just glad that I got this lucky chance to see the truth despite myself. I continually underestimated her capacity to lie. I guess I'm the proud new poster child for ostrich syndrome. I know I have a lot to work on about myself, and I plan to keep going to therapy (but alone this time). I think I'll be much better prepared for my next relationship, and I hope to find true happiness in that.
It's clear that she's going to keep love bombing me and try really hard to get me to reconsider. I'm not going to do that. But although I'm sure of myself, I don't doubt that it's going to be painful. I'm going to have to grieve for the relationship that I imagined I had. But I'm confident that with the support of my family, friends, and forum folks, I can get through it.
Oof. This is really no fun at all. But I finally have the clarity I craved for so long! That feels nice, at least.