I think most of us have dealt with this before. I know I did. Just keep your mouth shut for a while, and stay away from both of them. Your buddy will realize what he’s lost, and he’ll come back around eventually (as long as you don’t keep pushing the situation). If for some reason he decides to not come back around, then the friendship would have dissolved at some point anyway.
When this happened to me, it took 5 years and a divorce for my buddy to see the light and come back to his friends.
Ugh, I remember that story... What an awful time that must have been.
Thankfully I have a best friend who gets along great with my wife, and I get along well with his wife, so we can all hang out together and have a nice evening with sushi, a movie, or a board game. I think I'm pretty lucky there.
On the other hand, I have a good friend who's wife is just a know-it-all cocky blowhard bitch. She thinks that everything you have done, she has done ten times better, and she loves to interject her opinion about everything in every conversation. My buddy regularly bitches to me about how his wife can never be wrong or admit fault in an argument, so you can see what kind of woman she is (and what kind of man he is for not saying something to her about how he feels). My wife hates her, and I really can't stand my buddy's wife either. The straw that broke the camel's back was one night when she came over to my house and started talking all kinds of shit on law enforcement personnel, just putting down everybody from the police officers to their wives and families. Because this girl is a Marine's wife, she likes to brag about how her life is harder as a military wife than any other wife in the whole fucking world.
I kept my mouth shut out of respect for my buddy, but my wife was turning red. Finally, the evening finished and my wife told me that she never wanted to see that woman again. I agreed with her and told my buddy that his wife is never allowed in my house again. Now, we don't really talk. Such is the price of doing business.
My point is, don't make a man choose between you and his wife, because the wife will win every time. I still plan on seeing my friend, but definitely away from his wife. I don't know what you said in the email, but if you were able to maintain a friendship with your buddy for years while talking to him about how you did't care for his wife, and then one day you email her and suddenly the friendship is over, you did something wrong there.
Don't fool yourself into thinking your buddy didn't tell his wife how you felt about her. As Doc says, never underestimate the power of pussy. Your buddy probably put on his "friend filter" and told her in a much kinder way how you felt about her, and then when you sent that email you went laid it all out in such a raw fashion that she was just done with you.
I say you try to open up the comm-lines one more time, and if there's no progress, leave it alone. If he's really your buddy, he'll figure out a way to get his house in order and then come back and mend the fence between you fellas. Good luck.