How do I deal with a boyfriend who talks about his ex constantly when his ex is also his best/only real friend? They even hooked up sometimes after they broke up and had threesomes in another relationship of his and his ex plans on visiting some time and I don't know how to handle my feelings about this.

I very much want for him to be happy, but it makes me highly uncomfortable that she keeps being brought up constantly and that he still wants to have sex with her sometime (with me).