While Sapphire is now part of the small cluster of Others that the part-blood Diego has taken under his wing, Sapphire comes from the Outlands, not the Other-egg smuggling ring that most of Diego's Others come from. Diego was out doing work for the Black Market, and stopped to help an injured Other; Sapphire happened to see it, and decided to follow him. Any part-blood willing to help others was a good part-blood, as far as Sapphire's concerned.
He's been with Diego ever since, and because he has more experience with the outside world than the rest of Diego's little crew, and a stronger leadership mindset, Sapphire became the de-facto leader of the cluster of Others when Diego's not around (or unwilling to give them commands). Following Diego's loss of one of his wings, Sapphire's got the rest of the Others training in Suyis' holodecks and bettering their combat skills. Each Other has a skill lean that is tailored to their strengths, and designed to make up for any weaknesses and work well with the rest of them. Thus, they're much stronger together, but no individual Other is helpless alone. Fortunately, Sapphire figured this set up out on his own, and is pretty proud of it.
Now, maybe Diego won't run off and nearly die again.