The love ritual
The novel begins with a note that might strike the reader as ironic, because Mary is an English woman and a Christian, but she goes into the forest and performs a magical ceremony trying to convince her fate to bring her to her true soul mate. This is pretty close to witchcraft, and yet, Mary maintains her other English sensibilities throughout the story. The irony of her character is the she is willing to bend the rules, but only to get what she wants, not to explore a new way of seeing the world.
Hobomok, the suitor
Hobomok is the universe's apparent answer for Mary's question. Mary goes into the forest and says, "Show my my true love!" and then the universe sends her Hobomok, and she's like, "But not him." Why doesn't she like Hobomok? Among other reasons, the reader comes to see that she doesn't really see Hobomok as a decent suitor, because he is a Native American. His love for her convinces him that she is genuinely worth of love, but she doesn't love him perhaps because she doesn't believe he is fully human.
The timid savage
Mary believes that Hobomok is a savage, because that is the idea most commonly believed among her community, but when she goes with him on a hunt, she sees his true colors. He doesn't have savagery in his character. His love, the love he offers her, is sincere and universal, extending to the animals as well. He doesn't want to take life from another living being, which is a wake-up call to Mary. She wrongly believed that he was an essentially monstrous person.
Charles Brown's survival
Through dramatic irony, the story gives three years where Mary and Hobomok believe Charles Brown is dead. She receives a letter to that effect, and she breaks down. This irony is used to explore her attachment to Charles. Hobomok has to see how distraught she is without him. Through that time, the reader starts to see that she just doesn't really like Hobomok in a romantic way, for any number of reasons. Then, the dramatic irony concludes, and the reader sees that Charles Brown has survived.
The wrong wedding
When Mary was available, she was aloof and distant from Hobomok, but the moment Charles Brown comes home, she marries Charles. Hobomok is distraught by this instant marriage. All this time, she seemed unavailable, but she was only unavailable to Hobomok. Hobomok sees hypocrisy and injustice in her decision, because he loved her in a more deep and universal way than these Europeans love each other, but perhaps that is the value of this ironic disappointment—it shows two different approaches to love, and also more broadly, empathy.