When it comes to sex there is no such thing as a "normal". i'd say it depends on the type of relationship you have and, of course, the guy. Also, maybe you eradiate something that creates the idea in them of sharing you?I have dated three different black guys and in all of the relationships it led to me being shared with some of their friends. Is this a normal thing?
The only thing i wonder is why your question is about Black men in particular. i am a white man and would probably share you too. No difference there.