You are

Groaning, you collapse on her, pressing her legs flat against her slender body as she gasps and moans. Panting, you roll off of her, releasing her legs. She sprawls on the bed, purring happily, a look of lewd contentment on her face.

"I love the way you fuck me Mr. Carter, I love how you fuck me so hard. I feel like a woman, a real woman, not some stupid girl."

"You're a fine girl, Grace," you smile at her. "And I love fucking you."

"You won't abandon me, will you Mr. Carter? I couldn't bear it. I need you to keep fucking me. Using me. I'm your little schoolgirl bitch Mr. Carter. You can have others, but I'll always be first. Mr. Carter's first bitch."

"Listen to me Grace. I need you to listen. You have to be more discreet. You can't go pulling up your skirt like you did at breakfast. People will notice, and if they notice they might talk, and if they talk I might have to leave. If you want me to keep fucking your little schoolgirl cunt, you have to be more careful."

She looks at you with serious, wanton eyes, then nods, biting her lip.