Made of Honor (2008)

"It takes a real man to become a maid of honor."

Tom and Hannah have been platonic friends for 10 years. He's a serial dater, while she wants marriage but hasn't found Mr. Right. Just as Tom is starting to think that he is relationship material after all, Hannah gets engaged. When she asks Tom to be her 'maid' of honor, he reluctantly agrees just so he can attempt to stop the wedding and woo her.