I've been with my girlfriend for about 18 months and in all that time I've never cum while fucking her, only while masturbating in front of her. I think it's because, deep down, I don't really love her and know I'm only with her because leaving her would probably make her kill herself. This isn't an arrogant overstatement-she made several attempts when she was younger stemming from an abusive relationship at 16 with the man who would go on to father her child. She rejected the child and it lives with her parents, but that's a different story.

Before I met my girlfriend, I had been friends with her sister for years-she's engaged to one of my best friends. I have always been extremely attracted to her and our relationship has on occasion been very flirtatious, although never more than that. I would often masturbate while thinking about her though and to this day have a folder of pictures of her on my pc for this purpose.

Often when I'm masturbating with my girlfriend I'm thinking of her sister. She's more attractive, got bigger tits and has a larger body, which I've always liked. It's all I can do to stop from calling out her sister's name when I cum.

But my girlfriend will let me do anything with her sexually, so I can't bring myself to finish it.