Wow - he definitely has a bad track record. I have to imagine that he loves you and the kids but doesn't have hte guts it takes to be monnogamous. He's selfish - plain and simple.
The bigger problem of course, is that if you split up he will ahve the right to have the kids for periods of time and during those times you'll have NO control of what the kids are exposed to. Don't expect that he'll easily give up custody of the house either - he's a selfish guy and won't want to send a big portion of his pay to maintain a house he's not living in. So if you are planning on a divorce you have to prepare for a really difficult time.
All that being said, he's selfish, cares only about his "needs" (really "wants" not needs) and he wants to be a single guy. This is NOT about you - you could be the hottest woman on earth and he's still be like this - he has no character.
I wouls suggest that you confront him and tell him that since you can't stand looking at his face right now he's better find somewhere else to live for now until you can decide if you want to try to make this work. He has broken the most basic promise of your marriage covenant. Once he moves out give yourself and him a chance to cool down and evaluate what you want to do. Do not shut down any option. He may discover how lonely signle life is and may truly decide to change his ways. It IS possible - but it only comes from a heart change that is born out of trbouled times and reflection. He won't come to this conclusion living with his wife and kids and also hooking up with stupid girls he meets online.
Do not have sex with him again - get yourself tested for STDs. Talk to a lawyer about getting a formal separation agreement to protect yourself. But don't look at this as the beginning of the end of your marriage. Many people I know have been through really tough times like this and when they both came back after time away they were able to restore their marriage and build it stronger. But it does require that your husband get the heck out of your sight for now and you need time to really evaluate things. Don't make a decision about this when you're in the middle of so much pain.
And pray - God truly cares about the details of your life. This is not His plan, God's plan for your life is good. What some mean for evil, God can turn around for good. It's not hopeless. You can handle this difficult time - you can. You go mama - just prayed for you.