Ok I do not know the name of this movie and it is driving me crazy. Its about a brother and sister I believe the brother is getting married but the sister is falling for his fiancé. Anyone know it please tell me thanks.

I'm pretty sure that's Gray Matters. I haven't seen it, but I saw the box at Blockbuster and thought it sounded great. Cast is Heather Graham, Bridget Moynahan, and Tom Cavanaugh.