I made this comment/observation while back but not in the relationship context. My observation was why can't some Africans coexist in their country of origin and yet when they arrive in Western industrialized multi-cultural countries (mostly US and UK), they can coexist and go on about their lives with other people who are the total opposite of what they are culturally whether it is Black Americans, white Americans, Latinos, Asians in America. Pakistanis other Asians from the sub continent, Caribbeans, whites in the UK.
The response was that in their country of origin there is direct competition for resources/power whether economic or political. Continental Africans are not directly competing or can't compete with the other populations/groups of these western industrialized countries.