Oh yes they do

Steven stepped up behind Cassey and reached around her and began to caress her firm DD breasts. She felt herself being pushed forward as she tried to maintain her balance, on her high heels, as Steven began to fondle and grope at her massive breasts before pulling at her erect nipples.

"Oh Steven we'd better stop." the busty teen moaned as she felt her brother's massive erection now resting along the crack between her firm butt cheeks.

Steven leaned forward and began to gently kiss his little sister's ear lobe before working his way down to her soft neck.

"We'd better....oh." she moaned as she felt her brother's stiff shaft now being moved lower and was now resting against her smooth pussy lips. Slowly he began to slide his member back and forth along her wet slit.

Cassey bit her lip as she felt Steven's huge cock head now resting at the entrance to her tight little pussy. She knew this was wrong. It was **** and it wasn't something a brother and sister should be doing yet it felt so good to the hot bodied teen.

Slowly she felt her brother pushing the head of his thick prick into her and she realized that they weren't using any 'protection'.

"Steven don't.." she began, "this is wrong. It's ****."

"Come on." Steven snapped, "You know you want it. You can't tell me it doesn't feel good. Besides we're millions of light years from home in deep space. Who would know. It'll be our little secret. Just between us."

"I'm not sure......oh God...." she said as she felt her pussy opening up and her brother slowly entering her from behind.

He took his time as he allowed her to get used to his size.

"Damn you're so fucking tight." he said as he worked his large fuck took deeper into his sister's tight little pussy.

"Ooohhhh you're so BIG!" she cried out as she felt him bottom out against her cervix. She was well aware of the risks of unprotected sex but felt that they were two adults that could 'control themselves' before things got out of hand and went too far.

Steven began to move his hips back and forth as he began to fuck his little sister from behind.

Do things 'get out of hand'?

(Add threads please)