Girlfriend's Sister

I've been dating my girlfriend for a few years now and she lives with her sister, who is a year older. Her sister is very attractive. One day while my girlfriend was at work, her sister came into the living room clearly sexually frustrated telling me that she was mad that her boyfriend couldn't give her an orgasm. I told her that her sister and I always reached orgasm together. I could tell this furthered her frustration, and she wanted to know if it had to do with my size. I told her I had no idea, so she wanted to know how big I was. I told her average. She looked at me with a seducing look and told me that she wanted to see mine, to see how much bigger I was than her boyfriend. I told her no way, I was dating her little sister! She convinced me that it was just harmless curiosity and that she would never tell a soul about it. So, convinced, I asked her if she wanted to see it excited or normal. She told me she wanted to see it excited. I told her that something would have to make me like that in order for her to see it that way. She looked at me again with a look in her eye and without hesitation, slipped off her tank top and unhooked her bra. I immediately got excited, but I didn't tell her. She walked over to me, climbed onto my lap, and asked if it had helped. I couldn't lie and I told her it had. She said, "Good! Now let me see!" I told her I was still weirded out and that if she wanted to see it, she would have to take a look for herself. Again, without hesitation, she proceeded to look at my manhood. I am sure her boyfriend was small because she was shocked and she just sat there, holding it. I had to fight off every urge to make a move. I'm sure she wouldn't have minded. Anyway, she eventually got up and got dressed again. I put my pants back on and that was that. A few days later, she told me she had gotten a new thong for her boyfriend and wanted my opinion on it. I said sure and followed her into her room. Unexpectedly, she closed the door and pulled down her pants, modeling her thong for me. It was tiny, completely see-through, and to makes matters worse, she had just gotten waxed! My jaw dropped and I told her that I liked it very much. I told her I had never been with a girl who gets waxes, and she asked me if I wanted to touch! Once again, without expecting it, she grabbed my hand and put it to her body. I felt around, and was tempted to play a bit to gauge her reaction, but I didn't. That's all that's happened as of now. I'll keep you all updated!

— Alex, 23