I just finished the first draft of a new novel. It's not a romance novel, but it follows a relationship between two people. It ends with them splitting up after their relationship falls apart. It includes the viewpoint character committing acts of infidelity late in the story. One beta reader tells me I must rewrite it so the characters are together at the end. But I feel this would completely change the tone of the novel. I'm not sure what to do.

I want to get an agent with this novel. I'm trying to write it from the point of view of a fictional memoir, like the main character is using it to confess his sins. But I fear a lack of commercial potential for a book I want to get published conventionally. I'm kind of at a crossroads.