There are several texts which one could use to compare Joseph Conrad's story "The Secret Sharer" to.

1. Under the Trees: Written by Ashley Maker. Prince Thoredmund harbors runaway Arawy (she is running from an arranged marriage). His desire to help her outweighs any thoughts of consequences.

2. Blink: Written by Ted Dekker. Seth Border helps Miriam escape from an arranged marriage. Again, Seth (like Thoredmund) does not think about the full consequences when helping. While Seth is not actually harboring a fugitive, the story shows the impact a cry for help has on an individual.

3. "A Jury of Her Peers": Written by Susan Glaspell. A story of murder and evidence against the accused. Shows the compassion women felt for one another and why they would stand up fro another woman.

What literature can I compare with Conrad's "The Secret Sharer" for a paper?

This may seem a slightly odd choice, but hear me out. When I first read this excellent short story by Joseph Conrad, the text that I related it to was actually "The Most Dangerous Game." Why I thought of this text is because  both short stories contain two principal male characters whose interactions allow for self-exploration and development. Just as the captain is able to mature and develop by exploring who he is through his friendship with Leggatt, so Rainsford is able to define himself in opposition to the cruel General Zaroff, but is also forced to explore a darker side of his personality in the way that he has to play "the most dangerous game" and commit exactly the kind of murder that he protested against when he first found out about the concept of hunting men for sport. Both stories therefore indicate the shift of their protagonists from a position of innocence to greater experience in the ways of the world and the ways in which we have to sometimes compromise on dearly-held concepts such as truth and the sanctity of life.