well... if the relationship isn't over, then it should be.
my ex gf left me for my best friend, and being the shmuck i am i tried to ignore it *sigh* of course it didn't work..
my advice for a speedy recovery would be to give him a night and a day of completely selfish misery.. then get him drunk and agree with every petty bitch he has about her, but refrain from stating your own opinions, or you'll never hear the end of it
then, once the pathetic self pity seems to be mostly out of his system.. get him laid
best way to get over someone is to get under someone else