It was all a set up to make Wayne the man he wanted to be ?
I don't know if anyone mentioned it before but i got the feeling that Bill Murrays character had no intention of keeping the girl and set the whole thing up as a thank you for Wayne saving him, to force him out of his comfort zone and become the man he longed to be.
During his heart to heart with Murray he mentions the loneliness, the wanting to be a man and less of a coward or something along those lines. And i just got the feeling by making him fall for the girl and then trying to take her away it was all a clever scheme to make him fight for her, get his balls back and win the girl.
It reminded me a lot of how Jack Nicholsons character in Anger Management played Sandler to get him to become the man he wanted to be.