I think at this point you have to aid YOURSELF through YOUR ride.
Like when oxygen masks deploy during an aircraft emergency, you have to get one on yourself before you try to help someone else.
In light of your latest post, it might also be time to consider setting some boundaries in your situation.
Since she is with OM still, she has no reason to think you're suddenly going to morph into her best friend. It isn't rational. You're her husband and she's screwing around, torn by that fact or not, that IS a fact and it's ON HER. YOU did not make her have an affair. She made the conscious decision to do that. So while you are facing your own mistakes, make sure that's not on your list.
Now YOU have to decide how close you will let her get to you and you have to base it NOT on what you desire but what you know is BEST FOR YOU under these circumstances. Once you determine that, you set limits, whatever they may be for your personal situation. It won't be easy but it's important that you show self-respect as well as that new willingness to open up to her.
That's my opinion.
Basically to start straddling the fine line between standing up for yourself and being a doormat.
Good luck with it and don't worry about backsliding.
