ndfarmer, I'm just north of you by only a few hundred miles I'm sure... so I know what it's like to be in a small community where rumours take minutes for everyone to hear and add their own spin to...
The beauty of a small town is that one can dismiss a rumour of affair because a) it's a small community and too hard to hide, and b) it's probably a rumour started by a spiteful hater...
Unfortunately, affairs can and do happen in small communities and stay hidden for months and years...
Now let me further state, and I do this with most here, our small community (and it's less than 10,000 in our municipality / county) has had a number of murders, suicides, murder/suicides over infidelity just within my short 45 years on this planet...
Domestic violence initiated by the exposure of an affair is a very real risk... just ask your local PD...
Anyhow, having said that. Believe it or don't believe it, but what do you want?
Is an affair a deal breaker for you? I don't mean that she gets to stay in the affair and you live in an open marriage... I mean if you absolutely know she was having or did have an affair, would you be done?
Each situation is different, but if an affair is not a deal breaker, then if there is an ongoing affair, nothing is likely to get better until your W ends the affair. And forcing the issue is more likely to cause the affair to go deeper under ground...
So as labug mentions above, you really should get to your nearest book store and see if they have the Divorce Busting or (better; new and improved) Divorce Remedy book by Michelle Weiner Davis. Get it and read it.
If you are a God fearing man, then start praying for support and guidance from Him and put it in His hands.
Work on yourself. Keep living life as best as you can and in time, it will get easier. I'm almost 2 years in and it's been a lot of work, but it's worth it... My M has not been saved, but I am still M, even though separated for almost 1 1/2 years.
Season should be starting there for you, so busy yourself in doing what you need to do this spring and keep yourself distracted that way, as you keep working on making yourself a man that your W would be a fool to leave...
Read around here and learn from other's and ask questions and post often to keep us up to date. We are here to support you through this.
There's a list of 37 rules that hopefully someone can post that will help guide your behaviours from this point forward.
The more space you give your W, the less pressure she will feel and it can go a long way to possibly help save your M.
And detach from the drama... be respectful as possible, but be emotionally distant or void... that becomes easier over time... but you want to be in a state of mind that you act positively, rather than reacting negatively... that's what detachment helps us with...