Why does Cooper leave to go find Amelia at the end of Interstellar?

Christian's answer below is completely wrong. Earth didn't recover, they were on a space station. Remember how the baseball game and practically the whole town was curving upwards? It's because they were inside a space station. They even said it was named "Space Station Cooper" after the daughter, Murphy Cooper.

He goes to find Amelia to help her finish setting up the base camp for the new planet they're going to bring humans to. The point is that because Cooper sent his daughter Murphy the information she needed (remember when she screams "Eureka!" and tosses her paper?), it turns out Plan A actually worked. Plan A was to evacuate humans onto a giant workable space station. It was never workable when the original Dr Brand was alive because he didn't have the information he needed from inside the black hole.

He goes to see Amelia to continue Plan A, getting the new planet ready for human habitation. She's still young not because he's going back in time, but because they both stayed young due to relativity.

PS: The beings that created the wormhole were future humans who evolved to the point of being 5-dimensional creatures. That's why Coop says, "We sent ourselves back" and how earlier in the film young Dr Brand says he wormhole showed up just in time, as if someone was looking out for them.

Actually, it was Plan A that failed since Miller's planet was found to be uninhabitable for humans. Plan B was to fertilize human embryos on Edmund's planet in case Plan A doesn't come through.

After Cooper emerged from the wormhole, and was taken back to Earth, he finds that Earth has recovered from the blight that affected it decades ago. It is assumed he leaves to bring Amelia back to Earth since she no longer has to implement Plan B in order to maintain human life on another planet.

Because he's in love with her.

Can you say "duh"? I knew that you could.

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