If you're not a fan of the ending of 'Pretty in Pink,' you're not alone, and there's a reason for it! The current ending to the movie is not the original ending.
First, I'll sum up what happens in the final cut. Andie heads to the prom in the hideous monstrosity she likes to call a dress, and happens upon a very adorable-looking Duckie on the staircase. The two make up and walk into the prom as friends. Once inside, Andie sees Blaine, looking particularly gaunt and sickly, and those two make up as well, and Andie and Blaine live happily ever after. Duckie finds out that he's getting checked out by a hot blonde, and all is relatively well.
"But I wanted Andie to date Duckie!" Who didn't? Crazy people! Basically, the crazy people who made up the movie's first test audiences. Because of their extremely negative reaction to the original ending, which did in fact have Andie and Duckie getting together in the end, the cast was pulled back together to film an entirely new ending.
Unfortunately, what's done is done.