You have done a lot correctly but there are some points that IMHO need to be cleared:
As already stated, there is NO WAY you have ANY responsibility or accountability for her DECISSION to have an affair.
Let’s replace infidelity with another problem: Let’s say your wife wanted a new car and you refused because of money issues. We might even agree that you are earning less than you should be, or that you aren’t focusing on the budget or spending money at the tracks. That would not justify her deciding to rob a bank to get money for a car.
Her decision to cheat is the same logic: I need something I’m not getting and therefore I will get it from the OM.
The “correct” process would have been talking to you and establishing why she needed the validation she felt missing.
This is IMHO a key-issue: the state of the marriage (and therefore your input) did not make her decide to have an affair.
This is one reason MC won’t really help “affair-proof” your marriage. What needs to be dealt with is why she felt that need for validation. That’s internal – that’s all on her. If you ever accept that it’s your role to validate her and/or that something you did or did not do made her have to cheat… well… then there is the risk that something you do or do not do in the future will make her have to cheat again. She needs IC to get to the why.
Note how I hammer on the word DECISSION.
This is also a key issue; acknowledging that she decided to cheat. I’m not suggesting she woke up one Monday with the firm intention of starting an affair, but along the path from being friends to being lovers there are 100000000 decisions where she could have said “no”. At each and every one of them she went one step further.
Look – we aren’t surprised if a horse takes a dump in a parade. It’s only a horse and can’t decide where and when to relieve itself. We would be shocked if the trombone player in the band dropped his pants. Same with your wife. If she did not DECIDE to cheat but it only “happened” then there is no way she can decide not to cheat. It can happen again.
One “mistake” I think you might be making is demanding your wife is in the marriage.
How can she go from “I love you” and all that to total indifference towards OM?
One way is by remaining in the fantasy infidelity is. She’s thinking she needs to sacrifice the White Knight and riding on unicorns along the beach because the evil Ogre refuses to let her be happy.
This is reinforced by your obvious fear of divorce. According to your post your worst fear is being a weekend-dad, something you don’t have to be IF you were to d. But just like your WW makes the affair a fantasy you are making the reality of divorce a fantasy.
Let me be clear here: I am not suggesting you divorce. But I am suggesting you save a MARRIAGE or leave a façade of a marriage.
So, think again: Is divorce the worst outcome?
I challenge that thought. I think the WORST outcome would be to 3-6 months from now walk in on OM and WW.
If you don’t agree then my suggestion would be to not risk the marriage. Be safe and allow her and OM to have their romps. He’s clearly not leaving his wife and will probably be happy with a once-a-week poke in the supplies room.
If that doesn’t sound appealing, then RETHINK the worst outcome.
You want to LEAVE infidelity. Preferably with your wife, but then she needs to be 100% committed to reconciliation and the marriage.
To do that she can’t be allowed to have the SLIGHTEST vision of the OM being the White Knight. She can’t be allowed to think she sacrificed her personal well-being to save her kids from divorce or to save the OM family. Basically, you need to expose all her reasons for remaining in the marriage and peel them away until only one is left: Because she wants to be married to you.
To do that you yourself need to lose your fear of divorce.
You tell her she’s free to be with OM. You tell her D is the better of two bad options for you. It beats sharing her if she’s not in the marriage 100%. Ask her WHY she wants to remain married. Counter every excuse she uses except YOU.
You also need to understand what marriage is. You make some statements like never looking at her with the same eyes, lost respect, lost trust… If you think these are emotions that are there to be and/or if you don’t plan on building more positive emotions towards your wife then maybe D is your solution.