There is no single King Arthur story and no agreement on any symbolism that Guinevere might have in the Arthurian tales as a whole.
Among her abductors in different romances are:
1. Melwas/Meliagant/Meliagrance in various romances.
2. Valerin, in Ulrich von Zatzikhoven’s “Lanzelet''
3. Gotegrin, her brother, in Heinrich von dem Türlin’s “Diu Krône”,
4. Gazozein of Dragoz, in Heinrich von dem Türlin’s “Diu Krône”,
5. Brun of Moroiz, in “Duremart the Welsh”,
6. Lancelot, in various romances,
7. King Urien in the “Livre d’Artus”.
Among those who attempt to abduct her different romances but who fail are:
1. Bohort (Bors) of Gaunes in the “Prose Lancelot”,
2. King Lot in the “Vulgate Merlin”,
3. Mordred, in the prose Arthurian cyclic romances.
Among those called her lover are:
1. Yder son of Nut, in the Berrne version of “Tristan’s Madness”,
2. Lancelot, in many romances,
3. Gosengos of Lambale, in the “Vulgate Merlin” and the “Livre d’Artus” (who may be identical to the Gazozein of my first list),
4. Mordred, in early tales and later tales based on them.
In two of these tales, the abductor claims a prior right to have Guinevere as his wife: Valerin and Gazozein. Among the lovers, Gosengos of Lambale was Guinevere’s childhood sweetheart. Scholars see a similarity to the medieval Irish story of Étain. See http://en.wikipedia.org/wiki/%C3%89ta%C3%ADn .
Some scholars have even attempted to compare the abduction of Guinevere to the abduction of Persephone by Hades in Greek mythology, taking Guinevere as a goddess of summer, but there is no sign of anything similar in Irish or Welsh tales.
Some scholars see Guinevere as a mythical representation of sovereignty, who selects her lover who is king only so long as he keeps her favour. If so, in earlier Arthurian tales Mordred might legitimately win Guinevere’s love, and with it the crown.
In Chrétien de Troye’s “Perceval”, Chrétien has Gawain say of Guinevere (in Nigel Bryant’s translation):
“Truly, lady, she is so courteous and beautiful and wise that God never made a race or land in which so fair a lady could be found. There has never been a lady of such renown since God formed the first woman from Adam’s rib. And she is justly renowned: for just as a wise teacher teaches little children, so my lady the queen instructs and teachers everyone; all goodness stems and passes down from her. No-one can leave my lady without good guidance. She knows so well each person’s worthy, and what she needs to do to please him. No man does any good or honourable deed that he has not learned from my lady. And no man, however unhappy, leaves my lady with his mind still troubled.”
Can this be the same person who in Geoffrey of Monmouth and Wace abandons her husband Arthur for his nephew Mordred?
It should be noted that Guinevere’s relationship with Lancelot (in the “Prose Lancelot”) is partially excused because Arthur first breaks his marriage vows when he falls in love with a Saxon princess, though she betrays Arthur and imprisons him before he can lie with her. Lancelot, clad in Arthur’s armour, saves the day and rescues Arthur from prison. Then Arthur is deceived by Guinevere’s half sister who looks almost exactly like her who claims that she is the true Guinevere whom Arthur had married, but that the woman he is living with now was swapped for her on her wedding night. Arthur exiles the true Guinevere until eventually the truth comes out. He also intended to torture her before exiling her, but Lancelot came to her defence.
But in some other romances Lancelot apparently does not have an affair with Guinevere. In the “Lanzelet” by Ulrich von Zatzikhoven, Lancelot/Lanzelet has no love affair with Guinevere but marries four wives, one after the other, and then settles down with the third and raises a large family.
What Guinevere symbolizes depends on what the author of any particular Arthurian tale wishes her to symbolize, which may be no more than a Queen, or may be only herself as she appears in that particular story.