That doesn't mean you just have to roll over and be a doormat. There has to be boundaries and setting boundaries is healthy and good.
In my sitch I had to set 2 firm boundaries:
1) I am not going to tolerate being lied to.
2) I am not going to live in an open marriage or otherwise share my wife with any other man.
These are really hard.
When I first confronted my W about the EA I had to set (and then enforce the first one - "I know what is going on. Do not lie to me. Be honest"
I later had to firmly set the second one. "I am not going to share you with any other man in any way. I can not tell you to stop your R with him, but you may not continue your R with him AND remain married to me."
The second one is much more tough love and is really hard to do. You have to really mean what you are saying and be ready to take action to end the marriage if she does not stop. In my sitch, however, I do wish I had taken that stance much earlier than I did.
Me 42, W 39, S8, S6, S2 M 11y, A & ILYBNILWY 11/08 Walking away from a bad situation.