On a 7-9, she'll do it if you turn her on.

"Oh baby," you say, moving behind your hot girlfriend where she's kneeling on the blanket, "I know you hate swallowing my cum, but you know how I love it, how it gets me hot. And I'll make it up to you." You run your hands up Jenna's sides, caressing her thighs, her hips, bring your hands around in front to gently squeeze her firm breasts, while you whisper in her ear. "Now I'm going to fuck you, really hard, while your little sister watches. Do you want that?"

Jenna moans as you squeeze her breasts harder, and press your hardening dick against her ass through her dress. Little Jessie sits back on the picnic blanket, still trying to wipe your taste from her mouth. You grin at Jessie, as your girlfrind bends over, pressing her ass against you. Jenna supports herself with one hand as she reaches back with the other to hike up her dress, and pull her black lace panties down over her ass, and down her long legs.

Your girlfriend spreads her legs for you, on all fours in a public park, her little sister watching you both. You're hard again.