Arthur is married to Guenevere (Gwynevere) whose name is from an acient root (gwen-) meaning "white, pure."
http://www.reference.com/browse/Gwynevere
Merlin never marries, but is enchanted by Nimue, who may be a wood-nymph, or may be the witch Morguese in disguise.
http://www.legendofkingarthur.co.uk/legendary-characters/lady-of-lake.htm
Read Mary Stewart's trilogy of Merlin, Arthur, et al that starts with "The Crystal Cave."
