You make her like it, and she cums.

Jessie sits down on your lap, her back to you, her soft hair in your face, and rides your hard, thick cock up her pussy. Your girlfriend's hot little sister bounces up and down in your lap, taking your shaft deep, and moans as she rides you. "Oooh, fuck! Oh yes! Oh, fuck, yes!" Jessie reaches back to brace her hands on your thighs. You reach around to feel her little tits bouncing, and pinch her stiff little nipples.

Jenna watches the two of you fuck, feeling her own tit through her t-shirt, one hand pressed between her legs. "Ooh, yeah baby, fuck my sister. Fuck that little pussy hard."

Then Jessie throws her head back, arching her back over your shoulder, her long soft hair falling down your back. You feel her pussy constrict around your cock, flooding with her wet, juicy, teen orgasm. She moans and writhes and bucks, cumming hard. It's so good, you cum too, hard, bursting inside her, filling her hot sweet pussy with your seed. Jessie twists around, kissing you, sweaty, panting, and slowly slides off you. Your girlfriend looks so turned on, staring at her sister's pussy dripping with your cum.

(Mark +1 xp for making her cum)