He was already depressed. Knowing that it's all pointless does that.
And then you came along, and for once in a timeline felt something for him. Sans started paying attention to you.
Eventually, you two got together. It was a happy relationship.
And then you found out about timelines and resets. Suddenly the times he shut down or shut up made sense.
You picked up a knife to cut some food? He stops talking and leaves.
You fake-threaten him? Sans stops laughing.
It was odd, but you had to be careful. Eventually you were fine again.
But one night, he had a nightmare so bad, so vivid, he forced you to stay with Toriel for a few days until he was okay again.
For your safety, he told you as he shut the door with tears coming out of his eyes.
But then it happened again.
A third time. The worst yet, screaming and crying for hours as you got rid of every possible weapon to calm him, made sure Papyrus sat next to him the whole time.
But it wasn't enough. Despite soothing words and trying to get him or relax, he wouldn't allow you to help him.
So you broke it off, saying you were sparking bad memories.
Sans hated to know he caused the end of his happy relationship, but it was true.
You were like an iceberg, floating innocently among a still sea.
He was like a ship, moving along quietly.
You two stayed a respectful distance.
Then collided.
And while you were desperately trying to save him, anything left of the funny guy you once knew, it became clear to everyone.
He had already sunk.
