Hello Pfft. So sorry to hear that you're going through this.
It's taken me a while to post as your OP brought back lots of unhappy memories for me as about 10 months ago, I made a similar discovery about my DH.
We are working through things and it's been a tough time but I can completely identify with your anger, indifference to your DH and feeling that you might be better off alone. Before we had counselling, I also felt like this towards my DH.
I received some fantastic advice from MN (particularly WWIFN and AF!)and DH saw a BASRT accreditted counsellor. I had seperate counselling sessions with a wonderful woman and then DH and I saw her together. I'd never been someone who really believed that counselling would work but it really did turn our relationship around.
DH says that he never realised that what he was doing was so bad that he stood a real risk of losing his wife and family. He thought that if I ever found out, I'd give him the proverbial slap on the wrist 
As a result of the fall-out, he has totally changed pretty much all aspects his behaviour. He used to love his job but now he only works because he has to and spends every spare moment with me and the DC's. He is totally open and transparent about his phone, email etc and he has stopped socialising with certain people who we had identified as not being "friends of our marriage" (WWIFN's words I think!)
In short, I think we are well on the way to having the marriage and family life that we always wanted but it did take this awful, horrible time to realise that and take steps to turn it around. I can remember reading that a successful marriage is like a career - you can't just turn up and be present from 9 to 5 and expect to leapfrog your way to the top - it takes a lot of time and work to be successful.
There are still tough times but we deal with them as a team.
Take your time, don't make any hasty decisions and take strength from the fact that both you and he know that you could cope alone. When my DH realised that I thought I may be better off without him, he doubled his efforts to make things better. Your Dh does sound like he's beginning to realise the enormity of what he's done.
Would if help if I tried to list the things that we/DH did to make things better for us? It will sound v clinical but I struggled to think of anything when DH would ask, "what can i do to make things better" and I felt much more in control when I'd identified certain things that might help.