Need advice on cheating LTR that just broke up with me.

Am new to MRP. Just got on 4 days ago when my LTR of 6-years suddenly broke up with me over the phone. Have read NMMNG, WISNIFG, and am half way through Rational Man Year 1.

It's clear that I wasn't an alpha throughout the relationship. I'd say I was a mix, and oscillated between a beta and an alpha. There was also a fair amount of insecurity and controlling, which I now know I need to work on. I do well on finances, intelligence and general planning, but suck at shit tests (didn't even know those were a thing until now), and providing general direction (i.e. Let's go there now vs What do you want to do).

Pmed ScorcerKing for some advice. He gave me some and told me to post here for more. Decided to do so as a kick to the butt to improve.

The story: We are each other's first relationship. Of the 6 years, 4 of them have been LDR as we were at College. First two years were great. Things were slightly rocky when the LDR started. We had an initial agreement to come back and marry each other after college ended, but I wanted to stay and work in the States (I am not from the US) and so our initial timeline got shifted several years back. We broke up briefly because of this (she felt her trust was betrayed) but got back together a few months later. She wanted a break. I gave it to her. She came back to me three days later saying it was a mistake etc but I said no as I was pissed. Eventually realised I wanted her back and we got back together 6 months after.

Things seemed okay. Distance was tough but she seemed very happy when we were together. We travelled together during the holidays each year, which meant we saw each other about two months out of the year. Plenty of sex happened whenever we were together (at least 4 - 6 times a week and sometimes multiple times a day), and she seemed very happy. Then a year and a half ago, she cheated on me with a friend. Let's call him A. They were in a club, she got drunk and it happened. Was initially angry, but decided to make one last push to make it work. We agreed that she was to no longer talk to him. Everything seemed okay and happy again. Last week, she suddenly drops the bomb on me. She says she wants to break up, and that she has been thinking about this for the last 1.5 years but has never dared to tell me. Something snapped in her that day. I do not know why. She has not told me. I think it might be because I was badgering her to talk to me, as she is notoriously bad at digital communication. She said she did not speak to A for 8 months, and then resumed talking and discovered she had 'feelings' for him. She said she no longer sees a future with me and she loves A more, and wants to give things up with me to try it with him, especially since A is now coming back to where she is end of this year. This is after spending five supposedly perfect weeks that ended just a week before her admission, (again with plenty of bedroom action that made me feel things were going fine). She said she was 'trying her best to give it one last good shot'.

I am devastated. I don't know what to do right now. Part of me wants to move on, the other part of me wants this to work. I am currently working in SF, and am considering flying back to talk to her. We video-called briefly once since her admission to me. It was a short one since she started crying and turned it off because she said she felt too guilty and could not bare to talk to me anymore. At one point, she screamed "I am immoral" into the screen. She said she has already made up her mind and does not want to see me in person.

What are your thoughts on this? I do not understand the sudden switch or confessing of something she has been thinking for so long, especially when she seemed so happy and contented when she was with me. Do you guys think she really loves the other guy more? Thought of that kills me inside. Is this relationship already failed? Or can I still use MRP to try and salvage what I have left? If so, what should I do? I believe she is a good person, who made a mistake and no longer wants to deal with the distance and the guilt, and is acting out right now. What do you think?

TLDR; LDR Girlfriend of 6 years suddenly broke up with me. Cheated with me 1.5 years ago, and wants to go try things out with the guy she cheated me on. Very surprised because it was a sudden change as she always seemed very happy whenever she saw me (2 to 3 months of a year). Can this relationship be saved? Thoughts?