I was laying on my back, naked, my sister Abby was sitting naked on top of me. She had her knees either side of my hips and was riding my cock. Abby was sitting up, her tits bouncing as she rode me. I looked down between her thighs to see my cock disappearing into her shaved pussy. I was on the edge of my orgasm.
Suddenly the door opened. It was mom. Everything happened so fast.
Mom saw us, her daughter fucking her son, and her jaw dropped. Her timing couldn't have been worse. I had just started cumming and I couldn't stop now. My spunk shot into Abby's pussy. Abby screamed when she saw mom and jumped off me but I was still cumming. As Abby lifted her pussy off me I spanked on her pussy lips and then on the inside of her thigh. Mom was clearly shocked, she didn't say a word and left as quickly as she came in.
Abby looked as shocked as mom. "Shit! What are we going to do?" She asked.
"Don't ask me, you'll have to go talk to her."
"We'll both go. If we just explain she might understand, we're not the first siblings to fuck." I nodded in agreement and walked towards the door.
"You should probably put something on first." Abby said while pulling on a white, silk robe. I looked down at my naked cock then looked at Abby.
"You should probably wipe my spunk off your thigh." I said while pulling on a pair of shorts. Abby cleaned herself up then we went to see mom.
We went to mom's bedroom, knocked and went in. Mom was sat on the side of her bed still looking shocked. Mom, Janet, was 40, tall and slim. Her breasts were much smaller than Abby's but still looked a good hand full. Her blonde hair was cut shorter than Abby's, about shoulder length. Mom did have a few signs of her age but looked great. She was wearing a red t-shirt and a white, knee length skirt.
Me and Abby sat on the bed either side of mom. "We need to talk." Abby started.
"I can't believe you had sex with your brother. It's so wrong."
"It's not wrong. Sex is best with someone you love and me and Mike love each other."
"You love him because he's your brother not your boyfriend." Mom seemed more surprised than angry.
"I'm not her boyfriend," I pointed out, "I love her like a sister but we have fun together. Lots of siblings do it." I could tell mom was starting to understand. Me and Abby spent a few more minutes explaining everything to mom, except for me paying her. Soon mom had relaxed about the whole thing.
"Ok," mom nodded, "I'm not completely happy about it but if you two are happy that's good enough for me."
"Will you tell dad?" Abby asked.
"No, I don't know how I could tell him." Me and Abby left mom and went to finish our earlier fun, Abby didn't cum so it was only fair.
A couple of weeks had passed since mom caught us and mom had been very cool about it all. Mom never really said much to us about it and me and Abby were more careful to not get caught again.
One day I walked into the kitchen. Mom was in there doing the laundry. It was a hot day and mom was just wearing a yellow bikini top and some very short denim shorts.
"Have you seen Abby?" I asked mom.
"I think she's gone round a friends. Why, feeling horny?" She said with a cheeky smile.