If you like someone but you wouldn't say they're your friend, you might describe your relationship as cordial. Use cordial to describe a greeting or relationship that is friendly and sincere.
In Middle English, this adjective meant "of the heart," borrowed from Medieval Latin cordiālis, from Latin cor "heart." This core sense of "heart" can be seen in the synonyms heartfelt and hearty. The noun cordial originally referred to a medicine or drink that stimulates the heart, but its current sense is "a liqueur."