First: He deserves any and all aggravation he recieves for being stupid enough to ask his EX to something like a formal. Talk about frigging pathetic . .. hope he doesn't have sons to corrupt into half men like he is . ..
Ok so he's asks his ex to the formal in some loser attempt to keep her in his life and offer a chance of them getting back together again . . . and since she is obviously in the power position she treats him the way he deserves to be treated . . .
But then voila he meets a new girl that supersedes his Ex and so he is looking for an excuse to dump the girl he wanted to keep sleeping with, and replace her with the girl he hopes to sleep with . . . And he starts citing excuses like the ex is mean, which he already knew . . . That is why she is an ex.
Ok, I'm following now . . . First of all he doesn't sound like the kind of guy that is really strong enough to tell his ex he is going to take someone else in her place . . tough bananas, unless she really provokes him.
Oh well, I wouldn't be where he is at . . I would throw myself off a tall building first
But, he either needs to just cancel with her and cite the excuse she is being mean . . . although I would just flat out tell her I didn't like her and would rather take the new prettier sexier girl I met . . . or be like . . . look i'll take you if you promise to stop acting like a bitch because I will send you home by can in the middle of my formal if you irritate me . . .
But hey, thats just my two sense