As the title suggests, One More Night, is a song by Worlds End (Sekai no Owari) 

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Donghae closed the door behind him, looking at Hyukjae who had noticed the sullen expression on his face ever since last night. 
“I know you’ll be on a bus in a little
And you’re leaving without me” Donghae said, looking at  his shoes, he didn’t want him to go, but their short vacation had just ended, now Hyukjae has to go back to finish his service, leaving Donghae in Seoul.

“But don’t go away! Don’t run away for a little
How do I get you to see?” Donghae pulls on his backpack like a little kid, Hyukjae taking every piece of courage he has not to look into his eyes. They took the elevator for a moment they were silent.

Hyukjae opens his mouth “The truth is that I just want to be with you, And now I don’t know what to do” he admits, still not looking at the other. 
“But I’d do anything to steal a little time.” Half whispers, still hoping Hyukjae would stay,  his hope decreasing every floor down.
They get to the first floor. 

The door opens, and Hyukjae steps out, but his lover, took his hand to get his attention. “I need one more night” He looks up their eyes meet, and it crushes Hyukjae seeing Hae so close to tears, he knew Donghae hated being alone. “I need one more night!” He pleaded, still wishing Hyukkie would grant him his request. 
“Let me change your mind. Give me one more night…”  Donghae's words trail off as Hyukjae held his hand and lead him out of the building and into the streets, trying his best not to look back at him.  

“I don’t know how to say goodbye,
It’s obvious that I’m pretending to be fine” He blurts out, letting him know that he felt the same. He still wanted to sleep with him, eat with him, cuddle with him while watching some sappy romance movie. But they only have a little more time away from each other. What was two years if they’ll have all the time in the world after? 
Hyukjae train of thought was lost after he heard say. “But you’re here now. Now I have to try
To convince you to stay with me here for life.” He felt Hae making himself heavier as to slow them down. Hae understood how hard it was for Hyukjae to earn his vacation, and using it just to see him. He just can never get enough of Hyukjae. 

They arrive at the waiting shed, that was it, Donghae’s last chance. “One more night, just one more night” He said squeezing Hyukjae’s hand, crying. “I can’t say goodbye” realizing it, Hyukjae immediately gets up, and wraps an arm around Donghae, Donghae nuzzles onto his chest every word starting to get even more incoherent. Hyukjae buries his face onto Donghae's hair, and tries to soothe him.
“Give me one more night… one more night…” He says shakily, still hoping Hyukjae would suddenly drag him back to their apartment and stay. 
Donghae kept opening his mouth, still finding words to say, but nothing but sobs come out, as much as it tore him apart, Hyukjae resisted the urge to cry, without removing himself from Hae’s hold. He took his headphones and puts it on him, Hae looks up at him. 
“I know, a few days wasn’t enough. But we’ll see each other again, I promise. I’ll call you, every night, I’ll do my best so you won’t feel lonely.” Hyukjae reassures him, both hands on his tear stained face. “But please, for now, hold on a bit longer, a few months will be nothing after this.” He kisses his forehead, and a few moments later the bus arrives. They give each other a tight hug, Hae reaches out to him as Hyukjae gets in, but decides not to. 
Hyukjae smiles at him from a window and mouths a gummy “I love you.” He does his best to smile back. “I love you too.”
And he watches as the bus fades in to the distance.
“Just a few more months."