I'm a 24 years old girl and I'm in a relaion since two years with a 27 years old boyfriend. I love him and he loves me and our sex life is really great: we do everything and we keep experimenting new things.

That's said since a couple of weeks I have a sex fantasy that really makes me horny, and I keep masturbating thinking about it.

This dream is to convince my boyfriend to fuck my 19 years old sister while I watch them. Damn the idea of him fucking her in the ass, shaking her young, thin and perfect legs is so exciting to me, just thinking about it makes me wet.

I don't know why I have this fantasy, and I don't really know what to do and what to think. Am I mad? Should I talk with them about my fantasy? Should I just try to forget?

I would like to have your opinion.

:)