In Sir Gawain and the Green Knight, Gawain is tempted throughout the action of the text. By far, the most important temptation of Gawain's is that of his own desire to live.
Gawain knows that the only way that he will survive a blow by the Green Knight is to keep the belt given to him secret. Gawain has upheld his promise to the Green Knight on all other instances- the kisses given to him did not guarantee his life.
Gawain is able to be a true knight- he worships both God and his lord (Arthur), holds courtly love for both Guinevere and the wife of the Green Knight. (Courtly love does not mean romantic love, typically.)
Therefore, the temptations that Gawain must face are:
-the calling of a true knight in the taking of the challenge (refusal shows weakness)
-the holding of the promise to meet the Green Knight in one year (refusal shows dishonor)
-the promise to give the Green Knight all he receives while staying at the castle (shows honor to ones lord)
-the exchange of the blow (shows knightly honor)
-the sexual temptation of the Green Knight's wife (shows willingness to accept both God's law and respect of ones lord)
In all but one, Gawain is able to overcome the temptations that he faces- the inability to give up the belt.