Maybe I see this form an entirely different perspective. I am mot trying to upset you just trying to provide another POV so maybe you realize he is not being a horrible person on purpose and I am sure there is a reason he was chose as BM by your DF and they have been friends all your years.
People are really struggling finacially right now and perhaps somethign happened that you don't know about where he just now realized he can't afford to come. He was counting on a bonus and ot has been revoked by his company. He is no longer making commisons because the economy has been tough. Perhaps his job told him he can no longer take the time off and if he does he will be fired. I know this is hard on you but the bottom line is he has to be able to provide for himself and pay his bills and his mortgage etc.
Granted I don't know all the details, but I think we all get so caught up in our weddings we forget people have other lives and famileis etc and forget they have other priroties that do come first.
I agree it totally sucks you are now just finding out and I am so sorry about it but I have to think that there is a reason he just now told you guys. And I have to think there is a reason he was chosen as BM in the first place and try to focus on that. I am sure your DF is upset so instead of riling him up and making him more upset, try to support him positivley this way and say that there has to be a reason he cancelled like this and to remember why they were friends in the first place,. ya know?
Good luck, and regardless and I am sure you will have an AMAZING Wedding!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!