Overall, I think Kirshenbaum's book is a very good one for couples struggling with an affair. What's missing from my perspective is the foundation of "secure attachment" (you can read about it in many of my blog postings as it is the basis from which I work). Secure attachment is the antidote or insurance to prevent affairs.
What I find useful in When Good People Have Affairs:
1. Understanding that good people have affairs, and this doesn't make them bad people.
2. Kirshenbaum's tone of voice is caring, experienced, and practical.
3. The list of 17 different types of affairs, why they happen, what it means, and how to deal with it (although lack of secure attachment underlies all of the 17 types).
4. How the affair came about and what might need attending to in your relationship.
5. There's a long section about how to decide which partner (or neither) is right for you (if you dropped your affair like a hot potato when your partner found out, this section may not pertain to your current needs).
6. This book is a great tool for those who need it. If you do need it, please know that your need for self-care and self-soothing is very high right now. Your emotional (limbic) brain is triggered and on "high/overload."
Practice simple acts of kindness for yourselves:
Drink lots of water (alcohol is a depressant)
Exercise, or at least go for walks
Reach out for support from those you trust
Eat healthy foods
Breathe deeply from your belly
Listen to music
Be in nature
Notice your feelings and bodily sensations
Take breaks from dealing with the affair
Think of things you normally like to do, and do them (even if your heart isn't in it right now)
Couples do recover from affairs; it's up to you to work through everything and then decide whether you still want to be with your partner. Seek help if you need it (most affair situations do need help).
Best of luck (and work) to you both.