Note: several of these contain spoilers for the whole first season.

Earthly & Aftermath
(1829, 1830) Merlin/Arthur
Beyond
(1741) Merlin/Arthur
Hats
(200) Merlin, Arthur
Clad in Shadows
(1758) Morgana/Gwen, Gwen/Arthur, Gwen/Lancelot
Tradition
(1675) Merlin/Arthur
Sceptics
(945) Merlin/Arthur
edge of the coin
(1646) Merlin/Arthur
A Life Worth...
(308) Tauren, Morgana
Curse of Gifts
(4772) Nimueh/Uther