David Larrabee (William Holden)’s Timeline and Summary

David Larrabee is a lazy good for nothing, with oodles of money.
He drops out of a bunch of schools and has a bunch of disastrous marriages while chasing various women around and ignoring the family business (run by brother Linus).
Sabrina, the chauffeur's daughter, is in love with him, but he barely knows she exists. She goes off to Paris for two years.
Linus arranges for David to marry Elizabeth Tyson for business reasons. David is cranky about it, but Linus heads the family, and David goes along with it.
Sabrina returns from Paris. David falls in love with her, because that's the sort of thing he does.
Linus doesn't want David and Sabrina to marry, so he tricks David into sitting on champagne glasses.
While David is recovering, Linus dates Sabrina and gets her to fall in love with him.
David is clueless, but when he recovers, he figures out what Linus has done, and is very cross.
However, David realizes that Linus and Sabrina love each other, and he encourages them to go to Paris together.
David stays behind and his marriage with Elizabeth goes ahead, even though it will probably make them both miserable.
Not much of a happy ending there for David.