I pick up my gf's sister from work everyday as she works and lives close to me. I have been fantasising about her for a while now. Recently I picked her up and while I was waiting for her in my car I started masturbating to the thought of her sucking me off. I came in my underwear as I wanted her to be able to smell the scent of cum when she got into the car. I saw her walking towards the car yesterday and I had been rubbing the tip of my dick and I could feel the precum, I put some precum on my lips and when she got into the car I gave her a kiss on her cheek as usual, she must have felt the wetness but she didn't wipe her cheek. I'm going to do this from now on, I'm so turned on by the thought of her having my precum on her cheek