1) How did you come to these justifications?
Like everyone else did, I got so wrapped up in my own needs, my own pain, my own struggles, that I failed to be able to see anyone else. Things in our marriage DID need work. I was hurting and struggling and so was she. But instead of leaning into her, and offering my support to her in her time of struggle, I instead climbed under an emotional rock and settled into "poor me" mode. My wife was living and working in the next city over at the time (because of business reasons, not relationship ones). Rather than do all I could to maintain the marriage despite the distance, or to help or even recognize her loneliness living along so far away, I instead chose to see myself as a victim. Rather than hear her and see her and support her through her struggles, I ignored them, couldn't even recognize them to be honest. And sure, there are many moving parts to this story. But in the end, I chose to justify my affair on the simple premise of believing that my needs mattered more than others. When the opportunity presented itself, instead of throwing my all into saving my marriage, I instead threw in the towel. It was never about what was lacking in my life or my marriage. It was about what was lacking in myself.
2) When did you stop believing them?
That was a process. "When" I stopped believing them was when I was able to gain my empathy back, and that took a lot of IC/MC work as well as enormous efforts, patience, understanding and sacrifices on my wife's part, as well as my family. The other thing that had to happen, and perhaps the main thing, was that I needed the ability to see myself, the real me. I didn't realize how much my own self-worth was based on others... required others, to love me. I had no actual self-worth, and the very concept of self-worth itself was foreign to me, scary even.
3) Have you managed to sit with BS and explain them?
I'll offer some advice here. While this is certainly something that you must do (well, unless your spouse says otherwise) I do urge you to be careful. Explanations can easily turn into excuses and justifications themselves, and even when they don't, sometimes they feel that way to a spouse who was just betrayed in the most unexpected and cruel ways. When you do explain, be honest, be open, be prepared to throw yourself under the bus completely and own everything. If you feel that things may either be volatile, or that perhaps you will unwittingly make things worse for her, then perhaps consider doing this together at MC.
4) I know some of my actions have permanently scarred my BS. As most of these are based on fantasy and lies. Do I have any hope of helping her?
Nope, you cannot help her. The damage you've inflicted on her is heavy, crushing, and sadly, it is now her burden to bear, and her recovery is her own. The best you can do for her is to not make things worse. Honesty and empathy may help in that regard, but you will have to take your queues from her.
Instead, focus on yourself. See a good IC and get to the root of how and why you came to a point in your life where you allowed this to happen. The truth is, the lies you eventually told her, are the ones you told yourself first. Figure out why you cheated. What was lacking in your, in your life, that cheating was supposed to fill? Or was it self-sabotage, and if so, why? Until you know the answers to these things, until you understand yourself intimately, you remain dangerous, not only to her and your family, but to yourself and others. Until you are safe... you are not.
5) What did you do to keep the justifications going?
Honestly, once they were in place, I went on auto-pilot. It is strange now, looking back at my daily life then, and who I was, and how I thought... The lying, the sneaking, the double life, the damage done... it became my identity. It was my daily reality. It was constant stress, constantly feeling like shit, constantly needing more. For me, it was just another addiction. Not to drugs or alcohol, but to the attention, to someone filling my need for praise, to tell me I'm special, to lie to me in the way I prefer to be lied to, and all for the price of giving the same back to them. Like any junkie, the lies and justifications almost invented themselves after a while. It was the cost of keeping my fix-up.
6) Have you managed to "deal" with the feelings of guilt and shame surrounding the bullshit you were feeding yourself?
This is a lifetime goal, in my opinion anyway. The short answer is, you first have to learn to accept the concept of loving yourself, of being someone worthy of love and respect, and having those things without requiring them from others. Once you have that inner fortitude, then you need to accept the fact that we are what we do. We can't go back and undo what we did and the damage done. So, at that point in time, we were people that we do not respect. We did bad things, hurtful things, and we did them on purpose, with forethought and intent, and then covered them up, stealing the agency from our spouses. However, harboring guilt and shame over those actions, serves very little purpose, and often does more harm than good. Shame and guilt should be a motivator, but we have to take care to not make them an identity. Living in shame often hurts our betrayed spouses more. They don't need us to "feel bad". They need us to stop being the massive assholes that betrayed them, pull our heads out of our asses and be human beings. The way you learn to forgive yourself is by doing all you can to be a better person. Be supportive and understanding of your spouse, and put her needs before your own, even to your own detriment if need be. Be honest. Be so very vulnerable with her (read some Brene Brown). Be there and never stop doing the work. You don't ever really forgive yourself, rather, you learn to be someone better as a result.
7) Is there anything out there to help me unravel all this crap?
Yes, time and effort. Keep reading, see an IC, come to SI and ask questions like these, and be open to getting some really rough 2x4's thrown at you now and then. When you do, learn to listen, and consider why people are saying such harmful things. I promise you, it isn't because they hate you and just feel like being mean. Most of us respond emotionally when we see others making the mistakes we made, and we can see them taking destructive paths that we took and knowing we were just as stubborn or misguided once too... and it is frustrating, so we get emotional. That's a good thing. You'll get honesty here is nothing else. Just remember, take what you need and leave the rest.
Oh, and one last thing. Expectations. Those are bad things to have. Try listening instead.