It's not racist if you're dating someone of one race, but still open (in future or in general) to date people of other races. If you only want to date one race or certain races, then that's racist because you're excluding people based on some arbitrary trait. Like if you find 0 members of a certain race attractive, that's racist because you're making a generalization about people. It's okay to have preferences or whatever as long as you examine the reasons behind them.
Racism - "Racism is a product of the complex interaction in a given society of a race-based worldview with prejudice, stereotyping, and discrimination" https://en.wikipedia.org/wiki/Racism Where do you see racist in a relationship between two people of the same race? Is it racist for an Asian girl to date Asian guys? Is it racist for a black girl to date black guys? Is it racist for a Latina girl to date Latina guys? Is it racist for a alien girl to date alien guys?
Do you see the pattern? Are you American or something?