You were a demon. Atlas turned you into a demon. You were his first follower, you had told him you wanted to live a long life, but with your sickness, you couldn’t, so he manipulated you and turned you into a demon.
Atlas was the creator of many more strong demons. He was the boss, you couldn’t even say his name or else he’d kill you.
You got sick of his antics and decided to team up with a group of slayers who are determined to kill him. Since you were good with poison, you helped them with that.
The plan was to make a poison that can successfully take Atlas down, then the others would kill him.
But Atlas found out. He did everything he could to manipulate you back to him. He was a very good manipulator.
You were in the demon world, Atlas somehow managed to convince you to get into bed with him. And after a long and tiring night, he was now trying to convince you to stop working for the slayers.
“Come back to me, they’re just using you” he whispers.