The quotation comes from John Milton's Lycidas, his lament for a young friend who drowned in 1637 when crossing the Irish Sea.
"For Lycidas is dead, dead ere his prime
Young Lycidas, and hath not left his peer:" [8/9]
"But O the heavy change, now thou art gone,
Now thou art gone, and never must return:" [37/8]
Eighteen-year-old Valentine Searle died of wounds at a Casualty Clearing Station in Belgium and was buried in the big hospital cemetery at Lijssenthoek. His mother confirmed his epitaph.