A successful marriage is basically an endless cycle of wrongs committed, apologies offered, and forgiveness granted, STH, all leavened by the occasional orgasm. If you're having such a hard time forgiving her for this piddling "betrayal," STH, you're not cut out for marriage and your wife may want to run away before it's too late.
Some people just love to hold onto their grievances and ignore any and all attempts at reconciliation - or even some kind of humane closure. Even when they were the original source of the trouble in the first place. And although people like that hurt other people immensely, they hurt themselves even more. Unless they actually want to grow old alone.