Zara left Nibiru when she was in her teens to study on Mahoroba. She still maintained ties to her family and friends for a while, but was keen to court the favors of those who could advance her education and fortunes later in life. Which is how she wound up on Terminus.
They're close-ish in age so we could say they knew each other as kids. Maybe her family fostered him for a bit? It'd be interesting if they lost touch and reconnected now, so very far from home. Zara pretends to be on the straight and narrow nowadays.