I fucked my sisters BF as well, the only thing is, I'm a guy. I can remember when she bought him home the first time, my pusle started racing, I just so wanted his cokc in my ass so much.
So, I was just at home one day, he came round, my sis was at work, he came in and rubbed himself against me, I could feel his hard cock. He pushed me upstairs and threw me on my bed, he went out for a few minutes and came back in with one of my sisters short dresses, a bra and a thong, he told me to put them on. Once I had got changed he slid his pants down, he was wearing a some of my sisters sexy underwear, he was so hard his cock was sticking out. He told me to kneel down in a doggy positing, he slid the thong I was wearing to one side and entered my ass. Fuck it was good.
He jizzed all over my back. I turned over and licked him clean. A few minutes later he was ready to go again, this time he slammed his cock down my throat, I coudln't do anything else, I was hard, I sucked him off whilst having a wank.
I now go to his place every other day, he has bought me some sissy clothes which I put straight on straight away. He has said he will finish with my sister, I just want to start going out with him as by boy friend, going out in my sissy maid dresses.
He did buy me a dildo as well, which just love up my ass. He has also got some cock sheets which I can use to sit on and just feel the fantastic sensation of having a cock inside me.