I agree with Chatterbug when she(?) says: Your reactions are based on your w's actions. You guys are in a cycle that needs breaking, and maybe that's what you are identifying and your answer is to bring out the big guns (ie ultimatum)...but maybe the cycle isn't as massive as you imagine it to be.
And, as I look at your perspective, I see this quite clearly: "....I have no idea what is going on between them."
That's it - you have no idea what is going on between them. Isn't this mind reading? Don't worry, I do this all the time too and I'm working on it. But try not to let your imagination run away with you. Reel your imagination in.
However, your W's attitude of her not changing a thing (and then actually not changing a thing) is pretty harsh.
So, there's a standoff.
Before giving the ultimatum, maybe you could try really encouraging her towards more and more dancing. It's an idea, and maybe see what happens. Have you resisted her going- even just pulling a face? OR, do you appreciate her dancing? Even though you don't dance anymore, and you don't attend the classes, do you think she is looking for appreciation in what she does? Do you guys talk at length about her classes when she gets back? Do you get excited for her when she gets a move maybe she struggled with? Do you know her struggles/goals in the dance class at all?
If it's what she loves, then it would be important to encourage that love by loving what she loves. That is - as MWD says - is real giving. You don't have to understand it all that much, just love what she loves.
With dancing, it's all about how much the body can do, how to perform. The thrill tends to be in the ability of the body to do certain things.
About the OM, not sure how to 'make her do' anything. It won't work in the long run even if she does agree. She has to do it herself. So, I think your option is to throw as much love at her as you can, and let her decide to change partners.
