My Obsession

I have a sexual fetish (or obsession) that keeps ruining my relationships. I love anal sex. With women of course. To the point I can rarely achieve orgasm from vaginal sex. I just haven't been able to find a girl into anal sex as much as I am. I get super sexually frustrated when I can't fuck my partner in the ass frequently. Vaginal sex and blowjobs just don't satisfy me.
Now to how this sexual fetich came to exist. When I was 16 years old my family moved and I had to switch schools. I made a few friends quickly, but a guy named Billy became my new best friend. Shortly after we started hanging out constantly he let me in on a secret. Billy had a little sister. She was only 11. She was cute, skinny with really long brown hair. Anyway, one day Billy's parents were not home. He led me down the hall to his sisters room. The door was open and Billy walked in and told her to "get ready". I was stunned when she stood up and began taking her clothes off. Not to mention Billy took his clothes off too. Billy got in a drawer, pulled out a jar of Vaseline. His sister got on her hands and knees as Billy began sticking his fingers in her ass. The he rubbed some Vaseline on his hard cock and shoved it in her ass. I watched as he fucked her. When he finished he told me to take a turn. Billy didn't know one fact. I was a virgin. From watching I was rock hard so I stripped and got behind her. Billy stopped me for a brief moment and gave me instruction to "only fuck her in the ass". As I began pushing in her ass Billy said " we can't get her pregnant, we would get busted". I fucked her ass and it was amazing! I instantly loved it. Billy let me fuck her ass any time I wanted. And i wanted it a lot! This went on for 3 years. When she turned 14 she began dating and wanted to stop sex with us in order to have boyfriends.
Now its my problem. I got addicted to her tight little ass. I have not been able to find anyone like her.