Introduce some motion into the equation.

You lean back into the chair and shift your hips upward, nudging another inch of your cock into Beta’s mouth. The feel of her lips sliding down over your shaft is fantastic, and when you lower yourself back to the chair, drawing your cock out again, the sensation is just as intense.

She holds her head steady as you push your cock again and again into her soft mouth. You move in short, slow strokes, taking time to enjoy the caress of her tongue, the warmth of her breath. She does not object when you rest your hands on her smooth green shoulders, or when you move one hand to the back of her neck. Carefully, you draw her head downward, closer to your hips, bringing her lips down another incredible inch. You don’t want to risk **** her by pulling her down further (you don’t want to start an interplanetary war over a blow job) but you keep your hands on her shoulder and neck, holding her as you thrust into her mouth, as your heart pounds and your breathing turns to gasps and moans.

Alpha and Gamma continue to watch, exchanging glances or occasional nods, drawing some sort of useful information from the proceedings. You look at their breasts, their nipples, their thighs, their pubic hair, and you have a vivid image of rolling in bed with all three of them, their green skin sliding over yours, your fingers in their hair, their hands on your cock, in one prolonged human-Martian orgy...

Your level of arousal is growing almost unbearable. If you were fucking Beta, you could grab her hips and drive into her with all your might, but in this situation, you have to be gentle, despite what your cock is telling you to do. You remove your hands from her and clutch the arms of the chair, thrusting faster if you can’t thrust deeper. Beta keeps her head rock-steady, and maintains the embrace of her lips around you as you bob up and down. “Oh, god, yes,” you groan, “oh, god … uh … uh … mmmm …”

Your lust overtakes you suddenly, and you shout, and your hips jerk, and your cock swells and spills its load into Beta’s willing mouth. You lean your head back, lifting your lips in order to keep your shaft deep between her lips, letting your cock throb and pulse and fill her mouth with your orgasm. Every slight motion of your cock against her lips is a burst of heaven, and you moan ecstatically.

The strength seeps out of you as the last drop of orgasm leaves your body, and you collapse back into the stuffed armchair. Beta hasn’t moved during your entire climax, and her lips still hold the head of your cock, providing a soothing end to the whole experience.

“How interesting,” Alpha says, and as if that were a signal, Beta slides her lips off your cock, drawing one last twitch and moan out of you. She looks at you, pauses, swallows deliberately, pauses again, then glances back at Alpha.

“No? Well, in the future,” Alpha tells Beta, “you can spit rather than swallow, if you prefer.”