It's basically a quintessential British romantic comedy but the primary love story is between two women. Here's the description from Yahoo Movies:
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In a singular moment of sudden awakening on the altar, everything changes for Rachel when she is suddenly forced to reconsider the meaning of happily ever after on entirely new terms moments before her honeymoon has even started. When Rachel shows up at the church on what promises to be a fairy-tale wedding day, she is thrilled to be devoting herself for life to her long-time sweetheart and best friend, Heck. That's when the unthinkable happens. In a moment that overturns everything in which she thought she believed, Rachel catches the eye of a complete stranger, the wedding's florist, and like a bolt from the blue, recognizes her soul mate. Though she moves ahead with the marriage, something has profoundly changed. Everything about life is suddenly in question; and Rachel and her brand new husband are thrust into a journey that is at once disarmingly funny, decidedly bittersweet and definitely familiar to anyone who has ever fallen--for better or for worse--under love's intoxicating spell.