Hi Chris,
I haven't read everything you've posted because this situation has festered a long time. The OW is a problem but it seems that if it weren't her, someone else would have come into the picture. That restless feeling gripping your husband is not simply due to her. He pursued her. It is actually wrong for her to be punished because a superior sexually harassed her.
Without going to HR, she could probably get a job somewhere else in the system. That is just a matter of willpower. For your husband the job situation is much more complicated. Having him change might create a lot of stress. How long is his commute to and from work? Is he on call many weekends? Do the other doctors in his practice treat each other fairly?
If one physician dominates or bullies the others into covering more for him than he does for them, then an office assistant who sympathizes with the doctor who is wronged can quickly build up emotional capital. If she took care to schedule things to make his life better and easier, he might have been drawn to her.
I've noticed that doctors have to compete with each other to have the staff on their side. Some of these situations can be toxic and lower quality of life on the job.
Doctors have good income and high social status. It is easy for them to get women. Office staff don't have anywhere near the education that most doctor's wives have. So, the affair with the clerk is a downward move. That doesn't mean that there aren't hot, cool, smart women among the staff but there is a whole dynamic here that is ugly.
Your husband may not want to divorce and marry her because her status is too low. Also, if you socialize with other doctors families, he may realize that the guy who marries the hot nurse or administrator will be shunned by the other wives as a bad example for their husbands.
I know a doctor married to a SAHM who was a classmate from med school. She never practiced, preferring to become the soccer mom. She is very smart and has her surgeon husband on a short leash. He works like a dog (ok, he loves sawing bones) but she makes certain that all his free time is consumed by family activities. He has to struggle to find time to work out and stay healthy.
She does take care of him in many ways and loves him, too, at the same time that she would watch him work himself to an early death. It is a possessive relationship. She has the power. If he ever had an affair her antenna would pick it up fast. If their marriage ended, it would be war. He knows she would kick his as$.
It is easy to scoff at this type of marriage but I think he considers it a good deal. He has listened to an administrator break down and cry at work because her husband was having an affair.
An imperfect marriage may be better than a hellish divorce. Your husband seems to feel this way. The fact that you lost weight and rediscovered your sexual desire has saved your marriage. He once had telephone sex with her. Have you ever thought about asking him to do it with you? Maybe when he is at the hospital and cannot see the last patient and doesn't have too much to do, you could try it, too.
Once I sat on a train. And by chance the woman sitting next to me was the mother of a doctor who had been in the service and had the same specialty that the doctor I described above had. She disapproved of his life style. She was part native American and knew the US from the its worst side, having grown up poor, oppressed and beaten down.
She did not like the way her DIL spent money, it was a kind of meaningless consumerism. Her grandchildren had never considered ordering something cheaper on the menu when going out to eat. Her son never had enough sleep because there was this work imperative. This lifestyle that did not sit well with her, but she took care not let slip her opinions because she had no doubt her DIL would freeze her out instantly if she were so free.
How does your husband view his work and lifestyle. Do you share the same values? Can you agree on what sort of life you want to lead? Does he want to write papers for journals? Improve his qualifications? Do you support him in this if he does?
Ask him what sort of life he sees for his children? Tell him that there are successful divorced parents. It is harder but it can be done assure him that if you do divorce, you will not let your children down in any event, i.e., you have values. If he thinks divorce is an option, has he considered how he will respond to the challenge? I think he expects to fail, given his hesitation. By indicating that you will divorce if he is not in, you are forcing him to face himself. MC is a good place to raise these questions.
I found it fascinating that he had been a bartender in a resort town and had scréwed at least 100 women. Did you learn this before or after you were married?