There is a lot of symbolism in "Love in the Time of Cholera," so your essay topic is a wise choice. The title is a good place to begin. Florentino's love/obsession for Fermina is compared to a consuming illness like cholera, which completely drains the victim. Florentino is love-sick and almost every action he makes is aimed at bringing him closer to Fermina.
The yellow cholera flag on the ship at the end of the novel is an important symbol. Fermina and Florentino are finally together, and Florentino resigns himself to her, his "sickness." The flag is a symbol of completely giving oneself over to something, whether it is love or a disease, willingly or unwillingly.
What about the role of sex and relationships in the novel? Florentino has hundreds of lovers. Are the affairs really meaningless? Do they numb the pain of Florentino's separation from Fermina? How do other characters use relationships?
Other symbols could include scents, flowers, trees, and writing.