I've only read the first few and last few responses. I'll read the whole lot later but I just wanted to say, if you are feeling empowered and he's feeling shit, make the most of it. Get to the solicitor pronto and get things sorted now.
I went to the solicitor quickly, when I was still in shock, I think, and it helped to be doing something constructive. I wish my solicitor had acted quicker than she did to make the most of exP's remorse as he soon started going back on promises and 5 months later we are still wrangling over maintenance.
The situation was made more difficult as I Facebooked the other woman, telling her exactly what I thought of her and that's when exP started being a total twunt. I don't think I was out of line, considering what she'd done but it got me in a whole heap of trouble and didn't make me feel any better. Resist any urge to contact the OW, please. Rant here and cry with your family and friends but maintain an air of cool, calm, collectedness in front of your ex (even if you want to scratch his eyes out!)
Remember, your husband has proved himself to be a liar. He's not the man you thought he was and you CANNOT trust him.
Will be back later when DS is in bed but for now, loads of love to you. It's a totally shit situation to be in and I know it hurts like hell. It does get better though, I promise. You are going through the worst bit right now and you have more shit ahead of you but you can cope, you will cope and you will be happy again, I promise.