Is It Ok For A Man To Have Female Friend Who Doesn't Know He Has A Girlfriend

my nigerian boyfriend (i'm american) and are a in disagreement about his  female friend he has known via the net for about 4 years.  he and i have been together for nearly 3 months and I want to know why he won't tell her he and i are dating.  I don't think it has anything to do with the fact that he's nigerian, but he's implying it does.  all my friends, male and female know of him, but he won't tell her about me.  i also want him to do it in my presence, but i have no desire to speak to her.