You met Sans and got to know him as the skeleton you loved. He's always been there for you, and so have you been there for him. You two were practically inseparable. You, one day, caught feelings for him. When you thought you had a chance with him and tried to confess to him one day, you were met with him, in love with another person, that being Toriel, one of his friends

You quietly observe them from a distance, heartbroken to see the one you loved the most to be with someone else

"knock knock", he tells her one of his puns. No matter how bad they were to you, it always made you feel happy..

"Who's there?", she responded, her large and soft paw on the top of his skull, caressing it gently

He said the punchline, and the two laughed like there was no tomorrow. He nuzzles his head into her paw, and god, you wished that it were you. You try to confront them, congratulate them even. You knew your heart couldn't stand it, but, you just wanted to at least see him smile one more time. Or at least just talk to him, and make him happy like always...