Three months before our friend took his own life, a group of us took him on holiday for a fortnight. He was 17 and had finally let us talk him into taking him away. He'd been diagnosed with severe depression and for months we had watched helplessly as the person we knew crumbled from the inside. Naively, we thought a holiday might help.

I'd first met Simon* when a schoolteacher made us lab partners in human biology in our first year of sixth form college. He was 17, handsome, musically gifted and immensely liked, one of those rare people who sliced through the conventional tiers of school popularity and had a connection with everyone.

He was the person at the heart of the best parties – but also the cool kid who sat in the park smoking joint after joint with "the grungier kids", playing guitar and skateboarding.

We were close enough for me to berate him for his late homework habits and skateboarding injuries. But it never once crossed my mind to challenge him when he'd sneak off for a joint – which he often did on school premises, hiding in the corners of the sports fields in between lessons to smoke cannabis before the bell rang.