You.

You hang in the void, just as before. You can feel the faintest sensations of Ava underneath you, wrapped around your cock, legs against your hips, face pressing against your neck. But it's as if it's a million miles away, happening to someone else. Instead, the majority of your attention is focused on that choice:

You or her?

As much as Ava seems into it, it feels... reckless to experiment on her without understanding more fully what was happening every time you came. And you're a little excited to see what's going to happen if you pick yourself again. The first time had pretty clearly gifted you your now apparently-irresistible cock; the second, you still weren't sure what had changed. But something must have. Right?

Regardless, you clearly need to pick one or the other. Being stuck in a timeless void for all eternity wouldn't be as fun as having sex with your girlfriend.

You.

Color flashes back into your surroundings as time resumes. As your hips jam forward, filling yet another condom with your cum, you feel like every muscle in your lanky, skinny body is pulsing with pleasure, right along with your cock. "Oh god!" You cry out, arching your back.

Ava is clenching her way through her own orgasm beneath you and seems completely lost to the world, so you don't have any way to know if she can see it, but you're growing.

As your muscles flex and unflex, you can feel them bulking up, putting on ounce after ounce of solid bulk. You'd always been "scarily skinny," as your mom put it, but now you were pretty sure that you'd never be called a bean-pole ever again. Your abs are hardening, your thighs swelling, your biceps visibly bloating with muscle. Nothing obscene -- you looked like you kept in shape, but wouldn't be winning any bodybuilding competitions anytime soon -- but way bigger than before.

Which was good, because you can feel yourself growing taller, too. Your toes are suddenly dangling off the end of your bed, and your arms seem longer than ever.

As your orgasm finally settles down, and you feel the changes grind to a halt, you marvel at your incredible transformation. Ava really looks like a pixie beneath you now -- the top of her head now nestles somewhere around armpit-level -- and you feel like a behemoth.

You're propping yourself up off the bed with your arms, and while it's not strenuous for your new muscles to hold your body weight up like that, it is a little awkward, so you carefully relax down on top of Ava, trying not to smother her as you do so.

"Mmmm, you're so good at that, stud," Ava murmurs into your chest. You give your slowly-softening cock another little flex inside her, and she squirms appreciatively. "Let's just stay like this forever."

"Sounds good to me," you quip in response. Your voice sounds ever-so-slightly deeper now that your chest is wider.

After another minute or so of you two of you just basking in the post-cotial bliss, you pull yourself out of Ava and flop over onto the bed alongside her. The whole bed-frame creaks slightly as you do so, and you wonder why you haven't bothered to get a bigger bed for your taller body.

Ava rolls over and snuggles into your side. "So, did it happen again?"

"Yeah..."

"What did you pick?"

"'You', er, 'me', I guess?"

Ava sits up and looks you over. "Hang on, lemme see if I can figure out what's different..."