Samantha, masturbating

You look in and look away. You almost can't help it. It's just instinct to look away when you've caught someone doing something private.

Then again, this doesn't really count as 'caught.'

But before glancing back into the room you make intense eye contact with your girlfriend who stands next to you, a big smile on her face. "This is..."

"Exactly what it looks like" She answers.

"This is really happening." You say, not sure if you're asking or just stating it out loud so it makes more sense.

"No Kidding. Happy Birthday hon." Katie whispers.

You glance back into the bedroom.

Samantha has slipped out of her sundress and is clad only in a pair of flower print panties. Her wonderful flesh is on display on top of your bed, amazing large freckle covered breasts, curly red hair, pouring down onto her face as her hand, buried in her panties, rubs at something with smooth, calm, intensity.

Katie peeks in too. She giggles. "Well I told her I'd be right back with you and she should get ready. So... there she is." Despite being proud of herself, you can tell that Katie is just as nervous as you are.

Excited. But nervous.

"Now what?" You say somewhat foolishly.

"Did you really just ask that?" Katie jabs you in the side playfully. "Now you go in there..." she has to pause to take a deep breath before she can say it. "and have sex with my best friend."

Hearing your girlfriend say that makes your manhood insanely rock hard. You're ready. There's no use delaying.

"What are you going to do?" You can't help but ask Katie.

She smirks and pulls her shirt up over her head. She is indeed wearing a very nice, lacy bra. Then she answers