The Best Man's wife knew months before that the wedding was on her birthday. Even if it is a milestone birthday there is no reason she cannot be reasonable enough to celebrate her birthday a week before the wedding or a week after. Many people do not celebrate their birthdays on the exact day as it may fall on a week day and therefore they will put it off for a weekend. The Best Man made a decision to be in the wedding party and it is up to him to deal with his wife. However, if this is going to cause a big problem for the Best Man then the groom should talk to him and ask him to make a decision so he can ask someone else to be Best Man.
