The speaker is addressing someone who saw a boy struggling and did nothing, and who now has to live with the fact that he is dead. The poem is a list of small details: slipping grades, anger, silence, hair loss, the sound of the scales every night, the constant mint gum. Taken together, they hint at a young person in distress, and the scales and gum suggest, though the poem never says it outright, a problem with food or body image. Taking away "everything he loves" is the one thing the adult actually did, and it only made things worse.
The tone is accusing and raw. The repeated "You noticed" works like a charge being read out, and the questions in the second stanza sound desperate. The blunt "Bullshit" in answer to "I didn't realise" shows the speaker has no patience for excuses. The final lines are short and flat, which makes the loss feel sudden and final. The mood is anger mixed with grief.