But for quite some time, they don't seem to think of each other very much. They have a lovers' quarrel when Leela's old boyfriend Sean shows up, but Leela remains committed to Fry. Our relationship is the best thing in my life, so I'm sure I'll enjoy talking about it with you. She finds him irresistible when he is covered with butterfly pheromone. Leela practically encourages him in this endeavor. Her response, that he forgot about her so quickly when he met Colleen, shows that she does indeed have some pain and jealousy due to Fry's instability. He does the right thing by her, re-committing to the dinner date.
Leela talks to Zoidberg about Fry, indicating that she likes him but is turned off by his immaturity.
So she spent decades not only grieving a terrible loss, but also believing that Fry had done something really immature, inevitably lowering her respect for him. When Fry gets embarrassingly drunk at Oktoberfest, which by now has become a stately and refined affair, everyone but Leela abandons him. He then goes on to fail miserably at defending her honor, in fact providing his opponents with ammunition and even inadvertently insulting Leela outright. In the previous episode, the Leela who lost him looked back and said that her time with him was the best time in her life. In a rare moment of continuity, at the beginning of " The Butterjunk Effect " we see that the relationship has followed a real trajectory and taken a step forward: Although Fry doesn't realize it at first due to his promiscuous time-traveling, Leela intends to agree to marry him.