A dying playboy has to expose the lying fiancé of a brilliant woman so she can find true love, but falls in love with her himself.

What's at stake for your protagonist? How will exposing the woman's fiance's lies help him?

Good points raised above by DPG.

What is his goal? What is the end result? The logline states he ends up falling in love with her himself but then what?

Hope this helps.

Why would the playboy want to rescue the woman -- before he's fallen in love with her? Why would he get involved in her personal life in the first place? What's the trigger, the inciting incident?