First, Gawain is brave. He is not afraid to face the Green Knight, even though he knows that the Green Knight is a powerful and dangerous opponent. Gawain also shows his bravery when he agrees to stay in the Green Knight's castle for a year and a day, even though he knows that this means that he will be away from his home and his loved ones.
Second, Gawain is loyal. He is loyal to King Arthur and to his fellow knights of the Round Table. He is also loyal to the Green Knight, even though the Green Knight is his enemy. Gawain shows his loyalty when he keeps his promise to the Green Knight, even though it means that he must sacrifice his own life.
Third, Gawain is courteous. He is always respectful of others, even his enemies. He is also kind and compassionate. Gawain shows his courtesy when he treats the Green Knight with respect, even though the Green Knight is trying to kill him.
In conclusion, Gawain does uphold the virtue of being a chivalrous knight. He is brave, loyal, and courteous. He is a true hero of the Arthurian legend.