In Sir Gawain and the Green Knight, Sir Gawain is tempted three times by the beautiful wife of his host.
The first time he meets her is on the morning after his arrival at her husbands estate. He lies late in bed and she enters his room without knocking. His hostess flirts with him outrageously and claims to have captured "her knight" exposing thereby her complete confidence that he will in every respect do whatever any damsel requests of him, as befits a chivalrous gentleman. Caught between chivalry towards his hostess and honor towards her husband, his host, he treads a razor's edge of words, "Gawayne behaves most discreetly, for the remembrance of his forthcoming adventure at the Green Chapel prevents him from thinking of love (ll. 1205-1289)" and in the end escapes by only having to receive from the woman a single kiss. This he "returns" to her husband when he arrives later in the day from the hunt, according to the agreement between Sir Gawain and his host. He declines to reveal from whom he had first gotten the kiss that he returns to his host, citing that such a revelation was not a part of the deal.
The following morning, the scenario is again replayed between Sir Gawain and his host's wife. She again steals into his room and tries to force herself on him. This time, she calls upon his reputation as a romantic and bids him to teach her of love. Sir Gawain eludes her net by declaring his hostess to be more educated therin than he and "Thus did our knight avoid all appearance of evil, though sorely pressed to do what was wrong (ll. 1525-1552)" He escapes this second meeting with nothing more incriminating than two kissses, which he again "returns" to his host.
The third and last morning's meeting between Sir Gawain and his Hostess is by far the most tempting. When she again comes into his bedchamber, their meeting is so cheerful and and gay that "had not Mary thought of her knight, he would have been in great peril (ll. 1731-1769)"
When it becomes clear that Sir Gawain will not give in to temptation, his hostess asks if he has pledged himself to another woman. He assures her that he has not, and that he has no wish to do so. At this the woman sighs with romantic drama and asks of him a token of rememberance, "if it were only a glove, by which she might "think on the knight and lessen her grief" (ll. 1770-1800)." Since Sir Gawain has nothing but the clothes on his back, he regretfully informs his hostess that he has nothing to give.
At this point, the woman decides to press a gift of her own on Sir Gawain. First she tries to give him a gold ring with a beautiful, shining stone. He insists that since he has nothing to give her in return, that he cannot accept the gift. Thinking that "'because it seems too rich, and ye would not be beholden to me, I shall give you my girdle that is less valuable" (ll. 1801-1835)." She gives him a green lace girdle that endows any man who wears it with invincibility.
At first, Sir Gawain refuses the girdle as he had refused the ring. However, when he learns that 'he who is girded with this green lace cannot be wounded or slain by any man under heaven.'(ll. 1836-1865)," his desire for self preservation gets the better of him and he accepts the gift and the promise to keep the same a secret.
In Sir Gawain and the Green Knight, Gawain is trying to do the honorable thing--he's fulfilling the promise he made as a young knight in King Arthur's court a year earlier. He's at Bertilak's castle, and Gawain has agreed to a dealwhereby Bertilak will give Gawain anything he gets while hunting during the day and Gawain, who stays behind at the castle, will reciprocate. The first day, Bertilak's wife makes advances toward Gawain, advances to which he does not respond. Bertilak brings gives Gawain adeer and receives one kiss from Gawain in return. The second day is much the same for Gawain, though the lady of the manor's advances are more aggressive. Bertilak brings a boar for Gawain, and Gawain gives him the two kisses he received from Bertilak's wife. On the third and final day, the wife gets very seductive and more forceful with Gawain, and he continues to resist her advances. She offers him a piece of jewelry, but he refuses. She then offers him a scarf, claiming it has magical properties which will protect him. In a moment of cowardice, he accepts that gift, as he's planning to face the Green Knight very soon. Unfortunately, he is less than forthcoming with Bartilak when he arrives. Bartilak brings him a fox, and Gawain gives him the three kisses but withholds the scarf. Your question asked for Gawain's reactions. In short, he acted as a man of honor--except for that moment of weakness when he accepted the magic token. Later, he sees it as a badge of shame, a mark against his honor.