Tucker, what riverside means id you're being a doormat and you're being used.
First of all, to protect yourself, cancel all joint credit cards. Move half the money in any joint bank accounts to an account with just your name on it.
Next you should start investigating. Do you have access to her email, Facebook, cell phone account etc? She may not be telling the whole truth about how long the affaif has been going on or how deep it is.
Buy yourself a voice activated recorder or two (VAR). Place one under the seat of her car with velcro. Cheating spouses typically feel free to talk to their affair partners when they are in the safety of their cars.
Last but not least, meet with a lawyer to find out what your rights are. You may even want to start the paper work (it doesn't mean you actually have to file!)
Last, since you know the other man (OM) you should expose the affair to his wife or girlfriend or anyone else you can think of. Affairs do not like the light of day (like vampires)
While I personally would not tolerate cheating - not so much because of the physical act, but more so because of the breech in the explicit agreement I have with my wife to be honest in all situations - I think the response that Toffer is advocating is a bit like putting the cart before the horse.
I think this because, clearly, OP loves his wife and really wants to see if there is a route to reconciliation for their marriage. It is possible to get things back in order after an affair (in fact, tucker, you should look at the discussion group on here that is dedicated to dealing with infidelity. You'll probably find people with a lot more experience in this domain than elsewhere).
Anyway, Tucker wants his life back with his wife. If he acts as swiftly and severely as Toffer is recommending, even if there is a possible path to reconciliation - it will never be revealed. This is because he will then violate their marital contract in a very different, but similar way. He will breech the trust. Especially be doing things like pulling the financial carpet out from under her, hacking into her privacy through email and illegal bugging (bugs, in a legal sense, require warrants - do they not?).
In fact, even though I think the counselor on here was on the right track - I am not going to agree that now is the moment for Tucker to lay down a hard ultimatum. Especially since the OM is a business partner of his W - it is required that she deal with him. He can, however, make some reasonable requests regarding that she come up with a way to validate that she is no longer sleeping with the OM ... and then observe her. If she fails to hold up her end of the bargain - then he should start making plans for leaving.
When he does, again, I do not completely advocate acting so swiftly and severely. First, he should get (a) a lawyer and (b) a counselor. He will need both to help guide him through the process. He should do this without making clear to his wife what he is doing. Because I agree that if she catches on, she may act swiftly to protect herself. Once he has both lawyer and counselor, then they will guide him in the appropriate steps.
This will, of course, eventually involve protecting himself by taking his share of the joint monies. For joint credit cards, he should call and see if he can get his name removed from the account (or whatever it would take to completely remove his liability for any charges she may decide to rack up while still thinking the cards are the responsibility of the both of them). He should investigate where he would live - maybe even start looking at apartments or houses (depending on his situation).
Ultimately, however, Tucker - I am going to advocate that you do not take either of the above guys advice in the near term. They both present valid actions that you should consider taking ... but, given your desires, you should first take a few steps to see if your W is willing to work on the marriage. If after some period of time (you decide how long you can take it, a week - two - a month?) ... you assess whether she is playing along and putting in a legitimate effort to save the marriage as well.
If the answer is no, then you have to decide at what point you are going to draw the line in the sand and act to preserve your own sanity and stability.
You can always find love again (once you get past this) ... but if you sacrifice your health and sanity, those are much harder things to get back (and will undermine your future ability to search for love in your life).
Best of luck