So, there was this girl who was bff with a good looking guy and they decided to get married at a certain age if they still were single; so they did. When they were having sex, they were laughing. After that they had a baby,and they got like in a fight so they were separated. At the end they realize they were in love even if they were best friends and that being best friends was the romance in their relationship.
It´s not "One Day", but the girl looks like Anne Hathaway (but it ain't her)