In this (cloak) Shirt

ALSO CAN BE FOUND ON A03!!!!!!
When Merlin returns after Arthur's death, it's obvious that he's devastated.
Gaius, Gwen, and the remaining knights see it, and the new of Gwaine's death doesn't help anyone.
Merlin becomes emotionally distant, and though he's still snarky and joking, there isn't quite that shine in his eyes.
Gwen tries to grieve with him, being his closest and oldest friend, but Merlin insists that he's fine.
Until he forces himself to clean Arthur's room, and the all too familiar memories he's been trying to forget come tumbling back, forcing Merlin to admit that he really isn't fine.
Based on the song "In this Shirt" by The Irrepressibles