I was given the same advice by my coach. In a nutshell I think the idea is to not seem like you are turning your back on your spouse during their crisis.
After our ordeal ended my wife has told me that the way I acted made it very clear to her that I was her best friend and that her place is with me.
OM turned out to be a liar and a cheat. If he's prepared to cheat with a married woman and break up a family, he is scum and it will eventually be obvious to your W. But at that point you need to be the best option in her mind, so that's why I believe the coaches have you work on friendship.
Friendships can burst into flames of passion. Look at what her old friendship with OM resulted in.
But don't mistaken being friendly with actually being a doormat. Friendly is how you would be towards a neighbor or an associate at work. Kind and polite etc
Doormat is doing everything she tells you too. Not sure if I'm explaining this well so hopefully others chime in with examples.
If she asks you to for example go mow the yard, you would politely say " oh sure, no problem, right after I'm done watching this show". So you do it but on your time and at your convenience. It's not she says jump and you say how high.
What were the issues in your marriage?
Do you think you guys got things worked out well enough after the first time this happened?
What's the marital start of OM?
Me, H-34 now 38 W-32 now 35 T-13 now 18 years M-6 now 9 Daughter 3 years now 7 Bomb 11/27/12 - OM 1 year in house separation Reconciliation 12/2013. Healed now 2017