How do you get a girl in to a threesome?

Just start a conversation about sexual fantasies. Ask her is she would like to have sex with another person. If she says yes, DONT GET JEALOUS. Its normal for a person to want to do that even if theyre deep in love with you. And after her answer say: "I would like to see you and a another woman"... If she's a sexual person she wont have any problem but if she's a prude be careful and think before asking her.