Do you think that being deserted on the island together changed their outlook on rich v.s. poor or do you think it stayed the same?
Also do you think that if they did end up together their relationship would work out? I say no because it would no longer be just them alone together, they would have the outside world interacting with them as well.
In Marxist theory, class consciousness, the self-awareness of the objective position that an individual has in relation to the distribution of wealth and power in his society directly influences the values he espouses, his outlook on life, his choices.
Being stuck on the island just the two of them, without any class relations they were free to be themselves in their uniqueness as individuals, without society imposing its demands on them. The island can be seen as a metaphor for the classless society (something akin to the state of nature in the theory of Jean-Jacques Rousseau, before the establishment of private property).
Returning to the real world, the world dominated by the capitalist mode of production, they are broken apart. He, being poor, could still renounce his ties, his family, in order to be with her (as people sometimes do). On the other hand, she would have had to give up on her privileges. She already knew she wouldn't do that, that's why she feared leaving the island, why she begged him to hide till the ship sails on.