I can definitely relate to what you are going through... Not sure if I should dole out advice (think I’ve made every mistake in Michele’s books) so I’ll just stick to what I’ve learned and what has helped me get through my separation and eventual divorce.
-Standing up for your marriage and committment is admirable and displays real strength of character. Be proud of yourself.
-There is absolutely nothing you can say or do to convince him to change his mind. Just live your life and focus on yourself, friends, family, etc.
-If he is having an affair, he will not focus on you or your marriage. His attention is focused elsewhere so you could be giving him the formula to cure cancer and he will still be unaffected.
-Staying calm or “taking the high road” does not mean you are condoning his bad behavior (affair, opting for divorce, etc.). Even if “he has it coming,” anything you do to get back at him/hurt him will NOT make you feel better.
-Focus on yourself and the great things in your life – friends, job/school, activities, and family. Just because your marriage is ending/over, doesn’t mean the rest of the world stops. Friends and family still need support, job/school needs attention, pets need to be played with, etc.
-Avoid your stbx's drama as much as possible and don't bother snooping.
-The decision to reconcile (or not) should be made from a position of control and maturity - not desperation. If you allow him back into your life, do it because it is the right decision for you. If you decide to move on and start dating again at some point, do it because you are ready for a relationship and not because you want to “prove something" to your ex or to your well-meaning friends/family who want you to move on asap.
Hope my rambling helps!
Me: 30 H: 31 Together: 8+ years, Married: 4+ years Bomb: May 2007 Divorce final Oct. 2008 No kids, 1 super-cute yellow lab