A young advertising executive, on a rebound, falls for the girlfriend of his close childhood friend and woos her till she yields; they carry out a clandestine affair right under the nose of her boyfriend till she begins to suffer from guilt and decides to call off the affair; but her boyfriend comes to know of the affair and has his own plans.

1-The Inciting event is when the protagonist's original girlfriend leaves him for somebody else.
2-The protagonist is the 'Young advertising executive'.
3-His goal is first to woo the girl; and when he succeeds she begins to have moral qualms and then his goal is to sustain / maintain the relationship because she wants to call off the affair and go back to her original boyfriend.
4-The girl's moral conflict about the affair constitutes the antagonism. He has to fight this.

I will redefine the log line: "A young advertising executive, on a rebound, falls for and has a clandestine affair with his best friend's girlfriend who begins to have moral qualms about the affair and wants to go back to her boyfriend."

Does this work?

Yes, thanks, I think it can be shortened: "A young advertising executive on a rebound falls for and has a clandestine affair with his best friend's girlfriend till she begins to have moral qualms and her boyfriend also finds out about it."

Does it work?

The story begins when he falls for the girl; that's Plot Point 1. The whole of Act II is taken up by their clandestine affair and the girl's moral conflict. The affair being discovered is Plot Point 2. And the Inciting incident is when the protagonist's original girlfriend leaves him for somebody else and that kick starts the story.