I think most experts agree that most affairs run their course, and end within 6 months to a couple of years. However, that statistic includes one night stands and affairs where there isn't much emotional investment at all, but more of an affair of convenience (for at least one of those involved). Affairs where both are emotionally invested have a higher likelihood of becoming more. That's not to say that those don't blow apart too- they do- just that a deep emotional affair is harder to break. I know couples who eventually married their affair partners and have been married for years.
It is for this reason, in part, that I advise you to take action more quickly. I know that you don't want to right now, and that's ok, I just wanted to define further where I'm coming from.
In my case, my wife's emotional involvement became deeper and deeper until she was ready to separate (the OM did separate from his wife for about a week until my wife dumped him to work on our marriage). Oddly enough, there were times I thought things were improving as we redid rooms in the house, did landscape work outside, bought new furniture. I thought these were signs she was committed to a future. Turns out she was preparing the house to either sell, or have him move in- depending on finances! My wife had tried to go NC with the OM several times during their EA (she said deep down she hated herself for what she was doing, but couldn't stop), but each time they would re-contact, the attachment would grow stronger.
Keep a sharp eye out. I don't know how long you want to wait before you expose this affair, but I was husband and father of the year for two years and it didn't change my wife's feelings about staying married. What it did (other than improving me) was make her feel like I actually could be an alternative choice to blowing up her life for a man she didn't REALLY know.
In the end, my wife made (finally!) a rational choice to stay with me, not an emotional one. Her emotions were driving her away from me. Your wife will have to do the same. You are the logical choice- you are the father of her children. Right now, she can live in a fantasy world with the OM, the man that she loves, and come home at night to the man she tolerates because circumstances dictate she has to- for now. The longer she has to plan her escape, the more resolved she may become to see it through, and the more difficult it will be for you to win her back.
I would at least plan a timeline of when you think you've put in enough "great husband effort" (what are you waiting to see from your wife to show you?) and decide how you will eventually confront this thing.
