The concept of a black man in a relationship with a white woman is a "thing" that people have an opinion on, and that opinion comes with an entire set of stereotypes, fueled by racist ideology, a complicated past, and sometimes even pop culture.
Kanye West once rapped about how successful black men will "leave your ass for a white girl," and then put himself into that box by marrying a white woman, furthering the pervasiveness of flawed, generic ideas about interracial relationships.
If I explain some racially complex subtlety of life to my white girlfriend, that's one more white person who knows why using "ghetto" as a pejorative is cringeworthy and offensive.
I've never gone out of my way to reject black women; I just have way higher success rates with white women.
I started to see what it really meant to be in an interracial relationship.