Dude,
Like a few others have mentioned, you seem to be putting a lot of attention on the incorrect party, and on the wrong things.
Firstly, it is your WW that made vows to you, not the yoga teacher. You say that you are a SAHD, and by the sounds of it, a pretty damn good one also. Problem, your WW is supposed to be a high achiever, and high achievers get drawn to other strong personalities. By letting yourself go, it had a likely subconscious effect on her that you are no longer a strong personality. If you have pride in yourself, others will have pride in you.
As it has been mentioned, your WW made choices that led her to her A. From your narrative, she is a strong minded and focused woman. If she really were that, then how would she be manipulated into making those choices that led to an A? Take her off that pedestal that you seem to be putting her on. A M is when both spouses have the same respect and level as the other. You have elevated her to an unrealistic 'goddess' level. Puh-leeze, that is melodramatic, and does not generate respect.
The 'consequences' that your WW's boyfriend had as a result of your letter is expected. What did you expect? His reputation would be tarnished and he won't be able to teach again? He did not drug or kidnap your WW. She went WILLINGLY. If your WW were assaulted, then more drastic action could be taken by them.
Ignore your WW's boyfriend for now and focus on your WW, or you will drive yourself insane. Strategize your next plan of action once you have settled things at your own home. Focus on one thing at a time. You cannot afford to multi-task now.
I am also one who suspects that it went way beyond a kiss or two. Highly likely that he had a home-run with her. All the deleted texts would have helped bolster her case that it was only a kiss, but she deleted it because she wanted to keep the nasty acts away from your prying eyes.
The second thing that was not that smart, focusing on getting the yoga mat back. Why? Is it a custom made one that cost gazillions of dollars? If you were truly spiritual, one basic tenant is that you do not tie yourself onto material things.
Whose idea was it to go get the mat? You WW or yours? If it was the WW, it is highly probable that she wanted to see her boyfriend again, for that romantic 'one last time' (barf). BTW, what was your WW's reaction when he r boyfriend was posturing with you?
Another thing to keep note: No Contact means NO Contact. It will not help by you asking your WW to contact her boyfriend for answers. Be a man and do it yourself. Don't send someone else to do your 'dirty' work, it just reinforces in their minds how weak you seem to be.
As long as the mat it around, it will remind both you and your WW about her boyfriend.