No, I was too embarrassed

We weren't supposed to act like this, even though I wanted to.

"We can't do that, sis", I muttered.
"Why not?" she asked. "No one would mind two sisters to be a little curious... I can see you're horny, Selina.

I had made my decision. And it was about time I tried to have it my way. I stood up before answering.

"I'm sorry, I can't!"

I walked away and went upstairs to my bedroom. When I closed the door, I leaned onto it, breathless, overwhelmed by desire. I regretted my decision as much as I knew it was the right thing to do. I sat down with my computer and tried to focus o, something else, at least to calm the raging boner that was forcing out of my panties.

I was still in my girl's clothes while I started watching a tv show. I had two episodes to watch, enough time spent for my mind to forget. Until the sex scene at then end started driving me crazy. I couldn't help rethinking my decision again. I thought maybe jerk off would drive out of my mind these immoral ideas.

About ten minutes later, I had opened fifteen tabs on my browser, mainly tumblr pages of people liking my posts. I often jerked off at what the people who reblogged me where adding as caption beneath the post. It turned me on to read what they thought when watching me fuck myself with a dildo, or cumming all over my masked face. What they thought about me. The words they used to describe the effect I had on them.

When I went through all the tabs, I was still feeling like I could find something more exciting to jerk off to. I typed in 'sissy trainer', and the first image was a crossdresser receiving a facial from a man, while a girl was rubbing his cock between her fingers. There was a caption :

"When your sister found out you were dressing in her underwear and use her dildos to masturbate, she thought you would enjoy taking her place with her boyfriend too. After fucking you in front of her until you cum, he came on your face, because your sister would never let him do it to her. So it seemed like he would start using you more often to release his manly needs."

That was it. The universe wanted me to do it. I didn't hold myself any longer, and started jerking off to that image, and picturing myself, Anna and her boyfriend Mike doing just that. I started my webcam and saw how hot I looked, still in the girly clothes my sister had choosen for me. She was so right. It felt like I owed her, actually. I thought again about how good she looked, too. I pictured myself masturbate in the living room with her next to me. Would she have gotten further than just watching ? Or did she want to touch me from the beginning ?

I stood up slowly, shaking with pleasure. I knew we were still alone. I got out of my room, into the dark hallway. I silently approched the door and listened if she was still awake? Thinking I heard a noise, I opened the door slowly and found the room lights off. Anna was in her bed, asleep. I entered anyway, saying her name in the dark, but not loud enough to wake her up. I walked closer to the bed and stopped. What if I didn't wake her at all ? Her clothes were lying next to her bed, and I could see her panties among them. I looked at Anna, and from that distance, I could see her blankets uncovering a part of her butt, and almost a nipple. But it was so dark I couldn't say I was seeing it. I was hard. I she woke up now, what would she say ?

I dropped my panties, and put on hers, just under my balls, and started masturbating. It was wrong, really wrong, but so hot. And she wanted that. I was doing it. But where would I cum ? I thought of millions of possibilities, like in her panties (with or without letting them on the floor), on her body, on her blankets, in my hand to lick it up, or go back to my room, or try to make more light to see better...

It was coming. I quickly knelt on the floor, and came on my panties that were lying there. And it was an amazing orgasm. I was shaking hard. And I knew there was so much of it maybe it was drenching the floor. But I quickly recovered and got back to my room after covering my tracks.