Honey, just leave them to wallow in their shitty choices and the rest will take care of itself.
If you start making moves to break them up, it will be way too easy for them to paint you as the bad guy, or a crazy bitch. They will bond over it, and it will likely have the opposite of the intended effect. Your trying to break them up will turn into the glue that is holding them together.
Many OW and WH's have this "us against the world" and "our bullshit lurrrve is worth sacrificing everything for" dramatic mentality that your efforts will only reinforce.
If you have some hard proof that he is cheating on her, or something like that, that is one thing-- you could always send it to her, anonymously, and let the chips falls where they may.
But, if you have to manufacture scenarios that may or may not lead to the demise of their relationship, it will probably come back to bite you in the end. You could end up with a restraining order slapped on you, which would be a fresh humiliation that you simply don't need.
Revenge fantasies are normal. But normal isn't always healthy. If you can, take the focus of them and their shitty, adulterous relationship, and focus on you and the new, bullshit free life that awaits.
Don't worry about hurting OW. In time, your WH will probably take care of that all by himself.
As strongbutbroken says 'DON'T PET THE DRAMA LLAMA".