I posted last night to just found out and detailed everything I know about my situation. first let me say I am not without sin and I may be projecting my past indiscretions on my wife.
I want that to be true and I have many indications that it is true.
Here are the facts. My wife has admitted to going to lunch with OM @ 6 times since last November. This was kept from me. She has apologized for not telling me but has some valid reasons to have made that bad decision.
I am responsible for not having met some of her emotional needs.
Right now it seems as if conversation and recreational companionship are the only needs this OM filled for her.
six lunches over six months should not end a 19 year marriage.
My problem is first it was once - then three times - now six as I snoop and find out more.
I know the OM and am contemplating contacting his wife - telling her it has come to light that her husband and my wife have gone to lunch a few times. That my wife was not telling me about this. That I have no proof that the lunchs were anything inappropriate or that either my wife or her husband are guilty of anything beyond casual friendship but I would like to be more positive that this is the full extent of the relationship.
My wife is a member of this individuals gym. She goes there frequently and wants me to go there too. She doesn't want to give it up and I don't want her to but I need to be sure there isn't more going on.
Should I approach the wife?

I have details of the places they went and phone calls that were made. None of the details really show that it was anything more than a casual friendship but my wife isn't foolish. If it were an affair she would be able to hide it.
My purpose is to ask the wife to help me verify that there wasn't really anything more than a casual friendship.

The fact that she was hiding it from you in the first place, then lying about it is cause enough for concern. You should contact OMW, she may know more than you, or she may just have different pieces of the puzzle. She may know nothing, but she will be able to provide another set of eyes going forward.

I think your plan is good, do not accuse them of anything you don't know, just express your concern about the secrecy and see what she has to say about it.

Know that many times BS's are in denial. She may completely discount you and not want to talk to you.

Time to put the voice activated recorder in her car and get the truth.

My exW was going to lunch with OM also in the midst of her affair.