My Gf And Her Roommate

I love my girlfriend, she is the sexiest person on the planet and I love fucking her. However, recently I've noticed that her roommate is very sexy and has incredible tits and figure. My gf has brought up a threesome before but idk how to tell her I want to fuck her and her roommate. Her roommate is a virgin and I would love for me and my gf to teach her how to suck a cock and how to take a big cock up her pussy. I would love her to suck my cock while I eat out my girlfriend. I would also like for her to watch and masturbate while I fuck my girlfriend