Boone Carlyle developed several relationships over the course of the series.


Boone and Locke
First Episode: "All the Best Cowboys Have Daddy Issues"
Origin: The two hunted together regularly.
Since Then: Locke and Boone formed a party to search for Ethan after he kidnapped Claire and Charlie. The two discovered the Hatch together and spent the next weeks trying to open it. They also hunted for boar together, sometimes with Walt; and when it bothered Michael, Boone defended Locke. Locke gave Boone hallucinations that helped him overcome his relationship with his sister. Locke caused Boone's death by sending him to the Beechcraft. A vision of Boone later guided Locke in a dream. Guilt of Boone's death appears to have plagued Locke in the afterlife. But Boone evidently forgave him, though his jokes eluded Locke, who had not yet awoken.
1x13-Locke Soup


Boone vs. Sayid
Origin: Boone noticed Sayid's advances toward Shannon.
Prize: Shannon's affection.
Fuel: Boone confronted Sayid about his relationship with Shannon, and Sayid stood his ground.
Resolved: Yes. Locke convinced Boone to let go of Shannon's harmful influence in his life. Sayid ended up speaking highly of Boone at his funeral, voicing regret at not knowing the man more closely.

In their flash sideways, Boone showed complete comfort with Sayid and Shannon's relationship. He worked actively to reunite them, even taking a voluntary beating in the process.

Sayid and shannon


Boone and Shannon
First Episode: "Pilot, Part 1"
Origin: Boone's mother married Shannon's father.
Since Then: When Shannon's father died, and Boone's mother inherited his money, Boone began supporting his step-sister. She began conning him for further money, repeatedly faking bad relationships so Boone would pay off the abusive boyfriends. At some point, Boone fell in love with Shannon, and she seduced him the night before Oceanic 815's flight. On the island, the two bickered lightly, and Boone tried to protect her from a relationship with Sayid. Soon before he died, Boone overcame his obsession with her. In the flash sideways, he helped reunite the two to awaken them.
1x24-Legalize Incest