I'm not sure that I can offer much advice since we're both only a couple of months into this. But I can tell you that separation really isn't as difficult as you think it will be. In fact, it seems a lot easier than what you're going through and it can be very peaceful. The main source of your pain is his affair and his attitude to the marriage. Whether you are separated doesn't really change much.
I know that you're afraid that your husband will run off to the OW if he leaves and never come back. I know that you're also afraid that they'll start bonding more than they would if your husband is with you. But I'm not sure that separation actually increases those odds. In fact, it might even decrease them because your husband might start to miss you and the kids.
Also you do get used to being alone and you even get used to knowing that your spouse is with the OM/OW all the time. And after you get used to it, it doesn't hurt as much and there are less of those little indignities you're facing.
