See Likkutei Amarim (Tanya, Part I), ch. 32, regarding the commandment for a Jew to always love his fellow Jew. In that case, if hatred is obligatory on account of an individual's stubbornness to continue sinning even after repeated rebuke from his colleague, the love for him must continue to be maintained as well. Although Gentiles are not commanded to love each other, this serves as a lesson for pious behavior amongst them as well (Seven Gates of Righteous Knowledge by Rabbi Weiner and Dr. Schulman, page 109).