[male sex slave]

I’ve been with my gf for a couple years now and I’ve always had a cuckold fantasy. I’m scared to bring it up incase the reality isn’t what I expected or she isn’t into it. Any advice from Bulls or Cucks? Anyone who’s not thought about cuckolding if you had to be one would you rather it was your friend fucking your girl or a stranger?, advice would be appreciated, happy to answer any questions