Oy, I know exactly what you're going through. My Dad moved us then left us for a girlfriend he moved her up here too. And for the wedding part.... Let him know exactly how you feel, let him know how much he's hurt his own family. And that whole crying thing, mine does that too.... it's a show as far as I am concerned. So do what you feel is right. Don't let him guilt you into being his bestman, if you want to feel free to do it, and if you don't do it... just remember it is his fault not yours...
-Nate