I am terribly sorry you find yourself here. You certainly have a lot on your plate (actually-you have a platter) at such a young age.
I'm no expert and while I agree that it is pertinent to try to understand your H's side of the equation, please don't fall into the trap of thinking it's all you. Some of his criticisms will be valid (we are all flawed) and some will be a pile of poo. My suggestion to you is to take care of yourself, focus on being the best you can be, and focus on your kids. They didn't ask for turmoil, so remind them how much you love them and care for them.
Chasing your h will he is in an active affair is auditioning for the role of wife. Don't do it. Think about what things you would like to change and do it-for you.
Mindreading is a time suck so while incredibly difficult, don't waste time trying to decipher what he thinks. Go see an attorney, because at the end of the day, you are responsible for your actions and your h is responsible for his. Protecting yourself financially isn't going on the offensive. It's called being proactive, smart, and logical.
OW-don't waste precious time thinking about her. Regardless of what happens, time marches on. Your kids will never be this age again and you want to treasure these moments. You will be surprised at how strong you are.
Hang in there! It gets easier:)
3 kids BD 12/15/13 (IDKIILY. ) Rope dropped Cirque du Soleil style D final 9-9-14 "Some people are born on 3rd base and go through life thinking they hit a triple." Barry Switzer