I just got done reading your thread and I think you really buried the lead in this story.
At first, I was sucked in by your W's "plight" at being a "neglected" spouse, but then you reveal that your wayward W is actually a therapist! That giant sucking sound you now hear is all of the sympathy that I had for her heading south.....
I can fully understand why your parents can't stand her now.
Also, you mention that you have something on OM that could blow him out of the water. I think I would wonder why I am still interested in someone who is still interested in a crumb like the OM.
Yeah, I know. Impossible for me to be objective here, but I'll try. I have oscillated in my attitude toward my M over the past few months. Our M was troubled, and I did fail my W in some important ways, especially in the areas of intimacy and closeness. I think the fact that she's a MC makes her expectations in that area very high, and I fell WAAAY below that bar.
However, I have come to see how she failed me too. I was blown away when she offered that up in one of our recent talks. In fact, if she's done one thing to get me back hooked, that was it. She said things I'd wanted to hear for years. For so long she'd been taking the stance that our problems were all my fault, so for her to own up to her role in them was so vindicating.
What I have on OM was really just a variant of exposure. He isn't married, so I didn't have that easy option. I would have needed to be more "creative".
The fact that OM pursued my W while she was living at home with me and our three little kids tells me everything I need to know about him.