Vagabonds.

Louis was shaking slightly, tears welling in his blue eyes.
"Louis? You okay?"
"Was that- th-the last time we'll see th-them?" He whispered shakily.
"For awhile."
"How long is awhile?"
Zayn doesn't reply, driving into a turn lane.
"How long!"
"I don't know!"
"They're going to be worried! They're going to think we've been kidnapped!" Louis yells, trying to keep the hysterics from his voice and the tears from his eyes.
"If all goes well, that's exactly what they'll think."

Or the one where Zayn and Louis see an opportunity to escape from all that they know, and they take it.