The following are some ideas about how the American dream intersects with love in this novel.
to the Dutch sailors who first saw it. He writes that to them it was
a fresh, green breast of the new world. Its vanished trees, the trees that had made way for Gatsby's house, had once pandered in whispers to the last and greatest of all human dreams; for a transitory enchanted moment man must have held his breath in the presence of this continent, compelled into an aesthetic contemplation he neither understood nor desired, face to face for the last time in history with something commensurate to his capacity for wonder.
This was a world that seemed entirely new and unspoiled, an Eden in which Europeans could start over and rewrite Europe's corrupt past by building a better society this time. This dream of righting the past is also what Gatsby desires. He wants to turn back the clock and start over with Daisy at the moment he fell in love with her five years ago. He wants to erase the years in between as if they never happened. As Nick tries to warn him, this isn't possible. Nick says to him,
You can’t repeat the past.
But Gatsby insists:
“I’m going to fix everything just the way it was before,” he said, nodding determinedly. “She’ll see.”
Gatsby has an idealized, romanticized memory of his time with Daisy as perfect, as if they were in paradise together. He wants to recreate that, but there is no going back. Too much has happened in five years, such as Daisy's marriage and the birth of her child. Gatsby can no more return them to the paradise of their early relationship than the Dutch sailors can rebuild Eden on the new continent, which is the American dream as Fitzgerald sees it.
Much as rebuilding the past is impossible, however, Fitzgerald says it is the dream we yearn for, ending the novel with the following image:
So we beat on, boats against the current, borne back ceaselessly into the past.
To structure your talk, you would want to first set up your thesis showing parallels between the American dream as described above and Gatsby's dream of recreating his love with Daisy. You could then move to pivotal moments, such as when Gatsby and Daisy reunite at Nick's, and Gatsby is convinced, as he says above, that he can remake everything. Another is at the Plaza Hotel, when it becomes clear that Daisy is going to stay with Tom. Gatsby reacts to that by clinging to the dream. You could mention such points, too, as Nick admiring Gatsby for daring to dream big, despite his failure.
In the end, it seems that Fitzgerald is saying the American dream is doomed to failure—for example, if we take into account a class system that keeps worthless people like Tom and Daisy at the top, then the Americans have not done much better than the Europeans at building paradise. And because of this class system, a person like Gatsby will never get his Daisy. And though Gatsby failed, Nick sets him up as a kind of hero.