Edited: When an seasoned womanizer transforms his female best friend from a clinger to a player and finds himself attracted to his new creation, but realizes the repercussions of his teachings is worst than he imagined. Don’t know if this one is better than my previous attempt.

I would try to shorten the first half of your logline, and use the space to expand on ‘but realizes the repercussions of his teachings is worst (worse) than he imagined.’

I would change your logline to something more like this: A seasoned womanizer transforms his female friend from clingy to player. He becomes attracted to his creation, who is now too suave and sophisticated for the likes of him.