Hillel was roughly contemporaneous with Jesus -- slightly before, in fact: he is believed to have died in AD 10. Maybe Jesus was quoting Hillel. (I had numerous courses based on Midrash -- albeit over 20 years ago -- at the Hebrew College, then in Brookline, MA, now in Newton; that particular story might have been also in the first-year book we used at BU.)
Samaritans are Jews. The concept of "neighbor" or someone "closely related" applies to them, so the idea of loving your "neighbor" would apply to them in the Biblical sense, but not to the Greeks and other Goyim.
The concrete question is who is meant by "neighbor." The convntional answer, for which scriptural suppport could be adduced, was that "neighbor" meant a fellow member of one's people. . . . Does this mean, then, that foreigners, men belonging to another people are not neighbors? This would go against Scripture, which insisted upon love for foreigners also, mindful of the fact that Israel itself had lived the life of a foreigner in Egypt. It remained a matter of controversy, though, where the boundaries were to be drawn. . . . It was [] taken for granted that the Samaritans, who not long before (between the years A.D. 6 and 9) had defiled the Temple precincts in Jerusalem by "strewing dead men's bones" during the Passover festival itself were not neighbors.
Benedict XVI, Jesus of Nazareth, pp.195-96.
The legend (or "recollections" of Talmudic rabbis) says he lived to be 120 years (BC 110 - AD 10), like Moses. However, the Jewish sources, while admitting that Jesus may have been influenced by Hillel, provides a broader answer than Hillel does (who only mentions the brother love among Jews).
Correct. The Jews were not allowed to be intimate with foreigners, to eat with them, etc. They were considered profane. Their food was "unclean." Their gods were offensive to the Hebrew God, etc. Moreover, Leviticus specifically states that a Jew may not own a slave who is a Jew. But owning slaves who are not Jews was like owning property. The slaves and their children were part of the inheritance. It's all in the Old Testament.
That's why no observant Jew would seek to equate Jews with Gentiles. That is simply part of the Christian myth that was fabricated.
Pope Benedict tells of an interesting detail that occurred in 6 and 9 AD, but I am surprised he doesn't say that formal schism occurred at the time of the Babylonian captivity, circa 6th century BC.