The entire thing is about her. Her feelings, her thoughts, what she wants, what she needs, etc, etc. The only times she really mentions you is telling you what you did wrong.
Not one time did she say anything about your wants or needs, what's best for the children, etc.
Obviously all this makes sense, since she's writing it from her point of view, and trying to explain where she's at.
The point I"m trying to make is, in all her years of 'soul searching', 'healing', etc, did it ever cross her mind to say "what can I do to improve/save our marriage?" From what I just read, the answer is 'no'. She also stated that she hasn't loved you for the last 8 years. So that means for 8 years, she's been emotionally unavailable, and probably putting little effort into the marriage.
Obviously you've made mistakes and you're not perfect. Nobody is. But you've essentially been living in a lie for a long time. The person you thought you were with didn't exist. For 8 years she's been planning an exit.
How should you reply? I don't know. The experts here can provide help with that. I'd just recommend not to get into a 'back and forth' with her about who did what. I also wouldn't apologize for your past mistakes. I'm sure you already did that, and it served no purpose. If it were me, I'd probably just write something like "thank you for the detailed explanation".
Married: 15yrs Ages: Me 49, W 44 Kids: S12 BD: around 4/14