Regarding the closeness of his relationship with OW, she is with a married man! That is not something a self respecting woman does. And if he respected her, I think he would want to start the relationship off on a proper foundation - not one where OW is pleading for him to get a divorce.
If we read about the OW and MLC, we learn the OW is a parental figure and he’s using her to work through his issues starting from where ever he was emotionally stunted. That is going to take however long it takes. Either he will outgrow her and wake up or he won’t and he’ll be stuck cycling through his issues.
Either way it is nothing you can control. And she is not worth a nano second of your time. She is not getting the man he was. She is getting a married man who is broken down and confused. They will use each other.
Continue to focus on you. You are the prize!
Me 41, H 47, M 15 yrs, S11, S13 BD 1: 11/4/14 we work on it; really I pretzel myself BD 2: 3/31/15 H goes down to "dorm room" 8/15: H back to MBR 10/15: H back in dorm room 1/18: H files, now divorced