This is why the "I'm just a kid" card/"I'm a minor" excuse is retarded 9 times out of 10. Minors at Zack's age are equally as capable of doing evil shit like adults can. Teenagers aren't babies, they know right and wrong, they know good and evil. They're capable of murder, assault, and life ruination, just as good as adults are.
Zack's not a precocious infant, he wasn't born yesterday, he's a degenerate sex-obsessed manipulator who knew how to get witless fools like Nairo into awful positions like that to extort thousands of dollars and satisfy his disgusting needs. He knew just what to do and how to do it so he could wrap Nairo around his finger and keep him as a paypig, with the power to ruin his life for good if he felt like it. Same as any Treva Throneberry or Nikki Yovino.
Nairo's situation is a tricky one with no real way of winning. The only people who know what happened are him and Zack, no one can tell 100% who's telling the truth, if it was mutual or if it wasn't. Though Zack's actions afterwards do show that Zack had the dominant role in this disgusting fiasco. In any case, however, Zack carries blame no matter what.
Let this be a lesson to any fucking scene with a major presence of minors, stay the hell away from them at all costs. It's a retarded idea in the first fucking place to even sleep in the same room as a minor you're not the family or guardian of. Always have multiple adults present, or, for the love of God, keep the kids with their parents.