Cathy--my own PMA is rotten right now, and I don't want to discourage you with my own stuff.
There are a couple of past experiences that I've had with the disease that I did want to share with you. Whether or not it fits in your case is up to you to decide.
Everytime my 1st H would really screw up when under the influence, he would try a period of sobriety. He would try to be super-nice to me and the kids (I think the kids began to believe that everytime dad got drunk and mean meant they got to go pick out whatever they wanted at Toys R Us the next day. I wouldn't last very long, though, and soon he would start watching me like a hawk--waiting for anything I did "wrong" for him to pick a fight about--then he would storm off, get drunk and the cycle would repeat itself again.
In the end, I was grateful that he had the disease. He became weaker, and I became stronger--so I could get away from him without having to live in fear of our lives for daring to get away. He was no longer capable of carrying through with his threats to harm us.
What was really my saving grace though, was that he met another woman who was a much better at being a co-dependent and putting up with dysfunction and abuse than I had ever been. Once he had a new victim--he started to leave me alone.
If your H was watching and waiting for you to "screw up" so he could run back to OW and he could drink--it has absolutely NOTHING to do with you. There is no winning in that game.
If he did go back to OW--it could be that he needs someone much sicker than you are.
As it stands now, you all of this is guessing. You don't know what he's doing or where he is at. Even if it is worse case scenario, I have seen some pretty far-gone people get into treatment and straighten out their lives--and it's only on you to know if that is worth hoping for.
In my ex-H's case, he went from bad to worse--and beyond. He is dying a slow painful death from his alcoholism. He is on SSDI because he has done so much physical harm to himself--so he doesn't work--he just drinks now and goes through days on end of blackout. Once in a while, he calls here on the pretext of wanting to talk to one of the boys--but starts being abusive to anyone who answers the phone. We call around the family members and warn that he is on a drunken telephone jag again, because he will try to go down the list of us, hitting redial over and over. Very, very sad.