I'm sure that these are going to get sparser as time goes on, but for now, I find that journalling helps. 
I have been thinking a lot about WHY what happened happened, not simply to find an excuse, but to find out about myself. Whether my BGF and I survive this or not, I need to know for myself WHY I did what I did, so that I can stop myself, and have friends stop me, from doing it again. 
1) Lust
I have a huge problem with lust, one that I don't think I've been able to recognize for how serious it is. I just kind of thought of it as a "typical guy thing." My BGF is a beautiful woman, but I found myself fantasizing about a bunch of other women. I would indulge in pornography, and in fantasies about women who I'd never want a relationship with, but who I think to be physically attractive. I thought this was a typical guy thing, or rather, I wanted myself to think this was a typical guy thing. I indulged those fantasies, which was a form of emotional cheating. I didn't discuss them with anyone. From now on, those fantasies have to stop, whether my BGF stays with me or not. I can't indulge them any longer, because the instant it becomes a potential reality, I risk myself committing the same sin I did three days ago. 2) Self-Regulation
Independent of my relationship with my BGF, I had been under a lot of stress over the last several weeks. I have grad school to worry about, a professional conference to attend to defend my thesis, there are family issues, friend issues, and I need to figure out my housing for the next year or so. All this was going on, and I just felt completely down and low, which is why I went out to drink. This isn't healthy. I'm done with drinking to the point of excess, doubly so when I'm down. Temptation finds us when we're at our weakest. I left the door wide open to temptation, and didn't bother to keep a check on myself. I need to be aware of this and get a handle on myself, especially when I'm stressed. 
 
3) Selfishness
I am a selfish person, pretty damn obviously. However, that has to change. I have to look past my own nose. I need to put my BGF before myself in all things, especially after my sinful actions. Everything I do has to be for her, and open to her. I cannot keep things from her, especially if I want us to stay together through this and on to brighter times. I have to be as supportive as I can, putting her feelings throughout this entire process ahead of my own, and always being available for her, as well as knowing when to stay the hell away. I have to be mindful of what will upset her, and know that whatever I do has the potential to do that. It's not my right to get annoyed or angry at her upset or pain, no matter how long it takes her to recover, but to help her recover from my evil actions.