"So you're leaving," is all Kurt manages out, his usual high pitched voice toned down. He can't believe this is happening. His best friend, his savior, his everything is leaving him. Letting him go like a piece of paper taken away by the wind, never to be seen again.
"I'm not leaving, Kurt," the Doctor said, tears pooling in his warm hazel eyes. "I'm just doing what I should've done a long time ago: letting you live your life." He looked at Kurt with a smile, trying his hardest not to cry.
There was a part of the Doctor that had loved Kurt Elizabeth Hummel; a part of him that still did. But the logical part of him, the part that he always tried to have overpower his emotional part, told him that it was cruel to just string Kurt along like that. Because he knew what would happen.
He and Kurt would be happy for their whole lives, just them traveling in the TARDIS in all of time and space. Kurt would age, his body withering with every year, every month. Every day he'd grow weaker, until one day, he would die.
When looked at it that way, one would call the Doctor selfish. He would push Kurt away so he wouldn't get hurt, so he wouldn't have to deal with the growing pain everyday that he would feel after the human died.
But that wasn't it. It wasn't even the tip of the iceberg.
Throughout their adventures, the Doctor had heard Kurt speak endlessly about wanting a family, a marriage. What everyone wants, really. A normal life. No matter how much fun they had traveling through time, Kurt would always yearn for a simple life. He was a city boy, longing for green pastures.
"I'm just letting you do what you want, no need, to do, Kurt. If you stayed with me, you could never have those things. I can give you time, space. I can give you the stars and moon. But I can't give you what you want."
Kurt couldn't say anything, the numbness in his chest taking over his entire body. "I love you, Doctor."
"Goodbye, Kurt."