Hi 4MB - I am going through a very similar situation. I am sorry you find yourself here, but know you are not alone and there are amazing people here who can help you through this.
I will write more later, I promise, but the single best piece of advice I received was to have NO CONTACT with my H until he agrees to end the affair and work on the marriage. It's hard - it's more than hard - it's heart wrenching. But for the protection of your boys and the love of your H, it's critical. Use a 3rd party that you can communicate through. DO NOT talk to him directly, invite him for conversations, etc. It may seem impossible, but it's not.
I don't know how to add my link (Allen, can you help with this?) but read my letters that Allen helped me with. I can send them to you later so you don't have to read through everything but I have to get ready for work.
More later, until then, hang in there. Know you are doing the right thing for you and your boys, and your H. Know that there are people here to help. And know that I've already said a prayer for you!
LH
Me:38 H: 45 OW:34 S:4 Bonus S: 12 and 16 2nd M for both Together 12 yrs M: 6 EA suspected: 5/10 confirmed: 7/2/10 Separated: 8/12/10