Give me more details. I can't formulate an opinion without more hypothetical info. How long did this hypothetical relationship last? Why did it hypothetically end? Was it a chaotic/violent hypothetical breakup, or was it mutual? What kind of hypothetical texts/talks are we talking about here- is it friendly conversation, or is he trying to get with her? How long ago was this hypothetical breakup? How hot is this hypothetical ex-girlfriend? What was the hypothetical relationship between this friend and the girl before the hypothetical relationship started? In general, though, I'd have to say if they were friends before you started dating, then its perfectly fine for them to still be friends. Only assholes make people choose between one friend and another. Other than that, I'd need the aforementioned hypothetical details before I can formulate a conclusion.