To begin to calm down and let go of the vengeful thoughts that beckon you to call his future wife and a scandal, or to come to the wedding and try to upset her. Think about that the scandal will not return it to you.
Realize that the disaster was accomplished. He chose not to you. Try to put up with this idea and just move on. No need to deal with samoedstvom compare himself with his future wife, and to think that he chose her because she is - perfection, and you - the empty space. Nothing of the sort! He chose it because love is unpredictable and capricious, and the usual logic can not explain it. Simply, he has found his love, and you have yet to come. Do not scold yourself and in no blame - you, more than ever, now require an inner strength and self-love.
Do not comfort yourself false hopes that they will not last together, and a few months, and be not drunk with the statistics of divorce. Especially do not expect to continue a relationship with him, and after his wedding. Even if a man would not be against such an option, think you, why is it necessary? Life is not so long, to be wasted on empty, nowhere resulting relationship.
Throw it out of your head and start life anew. Engage in new business, make new friends, new hobbies. Do whatever it takes to stop thinking about it and start a new life. Fully focus on creating your own relationship with your best man, and very soon the wedding of your former men would go to the category of minor events.