Jerking off in my room

I first head to the kitchen for a glass of water, then while sipping it I look at my step-mom through the patio doors. She is out there sun bathing, maybe she has even fallen asleep, so won't notice if I discretely slip away to my room to release a bit of pressure.

I get to my room, have a seat on my bed, pull a few tissues out of a tissue box and start to pleasure myself.

I decide to take my time, and images of myself and Millie flash through my imagination, my cock is between her big tits, in her mouth, and I see myself fucking her hard in a variety of positions.

I finally settle on a fantasy of me fucking my step-mom's tits on the sun lounger, and I start jerking myself of faster and faster. Then, my fantasy is interrupted by a sound, and I half open my eyes to see what it is, and then I see my step-mom standing in my doorway. She is not making a sound, instead just quietly watching me with a small smile on her lips.