Answers: 1. No! Do not tell her why you are not comforting her. Go back to Sandi's rules. Let her sort this out for herself. Be positive around her, sympathize when she's sad (say "that must be difficult), then go about your business getting on with your life.
2. She has moved out, right? So maybe time to LRT? I think that might be recommended at this point, but I'm no vet. As long as you've expressed to her in the past that you're there if she decides to work on the marriage, then you shouldn't have to reiterate that. Now it's time to focus on yourself, not her needs.
How to respond if she is in pain? Say, "I'm sorry to see you hurting so much. It must be a difficult and confusing time for you."
Keep in mind that you don't REALLY know if her relationship with OM is "light" or not. (Don't believe anything they say.)
She will be more drawn to you if you are positive and friendly but also focused on yourself rather than her.
M: 43 H: 39 D: 14 Married 15 Together 16 BD: 6/2014 S: 8/2014 OW revealed 10/2014 Instigated dissolution 12/2014, in progress So over it!