Make me feel Alive (Underlust!Sans x Female...
It's been a few years since the monsters had been freed from the underground. You can't say you hated it, though.
Sans had been one of the first monsters you befriended (only because of his sexual puns,) and he had introduced you to his group of friends. One of his friends, Grillby, caught your eyes. You had started seeing him more, and you even started dating! Sans supported this and was supportive of your decision to date his friend.
But, even after going through tough times, Sans had your back, and helping you through thick and thin.
And you trusted him, he was your friend!
But in Sans' view, you were more than a friend.
(author wink ((; )