Do I ask about the affair? Do I expose the affair?(I know she will deny it. She still talks to me about the OM assuming I'm buying they are just good friends). Do I wait till after xmas?
Puppy Dog tails is the affair expert here. Do a search on his name and read as much of his advise as possible before exposing. Lean on his understanding.
At some point, you will state something very similar to this:
"I will not live in an open marriage. Tell me the truth" You believe she will lie. When she does, You then state "I will not tolerate being lied to."
You want it all scripted out before it happens to you respond and not react.
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712
