You just can’t have your cake and eat it too. With your ex.
Would you like to be friends with your boyfriend’s ex? Really? Think about that for a second. There was a time when he had sex with that woman and thought he’d spend his life with her. There was a time he spoke to her in a baby voice and called her “Sweetheart.” It makes your blood boil, doesn’t it? So how come you think you can put your boyfriend through that?