S.D.
Sounds like everyone but your mom needs to grow up. Let it be. Your husband shouldn't have corrected the fiance and you should have known what would happen. Did you throw the party to get credit or to celebrate his birthday? I promise that if you try to help him "see the light" that his fiance is conniving, he'll turn on you, not her. Go to functions, plan you own parties. Let him continue to be the immature one who skips family gatherings. If your mom asks you to help plan something for him and/or his fiance, feel free to decline. But don't let them dictate when you see the rest of your family.