Trying to save my M. W not really trying though.

[Thinker]

Yes, I do suspect an A. But what should I do?

you either go lunatic or you go cuckold!

Better lunatic.

The error most people seem to make (indeed I think I made) is to be so afraid of losing your M, that you don't stick up for yourself.

And by not sticking up for yourself, you lose the chance to save your M.

If there is an A, the best answer is "You are a grown adult and I can not tell you what to do, but I will not share you with another man in any way shape or form". You may not continue to see him and stay married to me at the same time. If you continue the A, then please leave this house now."

You have to wait on saying this until you can say it in a calm strong and confident way - no begging, no yelling.

You have to wait on saying this until you really mean it and can follow through on the consequences, including throwing your spouse out, initiating D yourself, etc.
It forces your spouse to confront the full facts of what she is doing and the consequences of it.

When you say this, you have to be fully emotionally prepared to follow through immediately.

the sooner you know the truth the sooner you can deal with the situation effectively and make them step-up to the plate.

After my own experience, I fully agree.