A lot of you are missing the point.
Ben Has a great time with Sarah. She is wonderful. Interesting, exciting, smart,beautiful, adventurous. Everything every guy would be looking for. She is so wonderful, and he is so enamored of her, that he is willing to throw away his wedding, and the life that goes with it just to be with this amazing girl he has been traveling with for 2 days. He is willing to destroy all that is expected of him by his family ,and her family, their jobs and everything else for Sara. He goes into the wedding party location fully planning to bail out and get with Sara.
Until he looks at the woman who is going to be his wife.
He lays eyes upon her, in the midst of the complete and utter chaos going on in in the backyard, in his life, and in his head, and time slows to a stop. Nothing else matters. They are instantly on the same wavelength. The world and all their plans are literally being blown to tatters around them, and that is just fine once they have a moment to talk. All that matters is the two of them, and nothing else can matter.