Love Conquers All?
You can think of David in two ways: an irresponsible dirtbag that chooses a partyboy lifestyle over serving England on the eve of WWII… or as a guy so besotted by one woman that he gives up the throne for her.
The movie mainly supports the former character analysis and paints David as an irresponsible dude who unfortunately has a ton of responsibility—he's the eldest son of King George V. He actually has no interest in being king because he wants to marry an American woman who the royal court will never accept. When he finds out that his father is dying, he even thinks aloud,
DAVID (KING EDWARD VIII): Old bugger's doing this on purpose […] Departing prematurely to complicate matters.
In other words, David thinks his father is dying on purpose just to force him (David) to take the throne and leave Wallis. But as we all know now, that's not what happens.
When his father passes away, David mutters, "Poor Wallis. Now I'm trapped," which shows just how much he doesn't want to be king. He also wants to know why other people can marry for love when he can't. And we think that's a pretty fair complaint. As he demands to his brother,
DAVID (KING EDWARD VIII): Your beloved Common Man may marry for love, why not me?
England is about to go to war and it needs a stable king, but Edward walks away from his responsibilities and gives the throne to his brother Bertie. It's selfish, but it's also romantic. After all, David is giving up everything for the woman he loves. And that's more romantic than any number of heart-shaped boxes of chocolates or bouquets of roses.