Boundaries are a beautiful thing during this time of emotional chaos.
What do YOU need to feel secure in your marriage? Write it down. At this point focus on the top three.
Is he being a husband, watching out for your best interests, as you do for him?
Are you happy? Each individual is responsible for their own happiness, state of mind.
Read "Not Just Friends". It talks about how affairs unwittingly happen, when a member of the opposite sex becomes the emotional support for your spouse which weakens the marriage. Read it, read it, read it... it's great!
Their friendship, which her husband knows about is crossing boundaries. It's not about him and her. It's about you and him. How his actions make you feel. If you're busy reacting to what he does, you have no time to know what you need.
Set your boundaries. Do you want to proceed with a legal separation? What specific actions do you need to see from him.
With me, it boiled down to respect.
Your spouse responds to having his peepee whacked. Take a deep breath. Let go of the hairballs and goo. Focus on what is at your core. Go from there.
A legal separation puts everything on paper. Responsibility and accountability are laid out. Of course he wouldn't like it. Who wants to be told what to do when they've been able to do what they want?