What is the main conflict in Eugene Onegin by Alexander Pushkin?

Alexander Pushkin's poem/novel tells the story of two sets of lovers. Eugene Onegin, the hardened socialite, rejects the love of passionate Tatyana Larin, while his friend, poet and romantic Vladimir Lensky, falls head over heels for her sister Olga. Onegin's annoyance at Vladimir leads him to pretend to seduce Olga, and Vladimir challenges Eugene to a duel to revenge his love. Eugene kills Vladimir. In his sorrow, he leaves his country estate forever. Years later, Eugene meets Tatyana, now a confident, cold beauty, married to a prince. He falls madly in love with her; however, although she still loves him, Tatyana must reject Eugene as he rejected her years ago.