In The Great Gatsby, why does Wilson lock up his wife, Myrtle, in anticpation of taking her west?
A careful re-reading of Chapter Seven should help you identify the answer you are looking for. The appearance of Wilson with his "hollow-eyed" gaze and his general weakness certainly serves to illustrate that something is very wrong, and perhaps more than just physically with him. However, let us pay careful attention to Wilson's words as he explains why he needs some money quickly:
"I just got wised up to something funny the last two days," remarked Wilson. "That's why I want to get away. That's why I been bothering you about the car."
Thus we can see that he at least has become partially aware of the other life that his wife is living and has realised that their might be some form of infidelity involved in it. Consider the comment that Nick gives us after Wilson's speech:
The relentless beating heat was beginning to confuse me and I had a bad moment there before I realised that so far his suspicions hadn't alighted on Tom. He had discovered that Myrtle had some sort of life apart from him in another world, and the shock had made him physically sick.
Wilson has therefore discovered something of Myrtle's little secret, though he has not yet linked Tom with this secret. The shock has almost physically destroyed him, and has made him determined to move West quickly to take Myrtle away from the dangerous influences that threaten to tear his marriage apart.
George had known from early in their marriage that Myrtle held him in contempt. Her opinion of him had changed drastically a short time after their wedding when she discovered he had had to borrow a suit to get married and had not told her. George, she determined, was not a gentleman: ". . . he wasn't fit to lick my shoe," she said. Their marriage was a misery and George became a brow-beaten husband. As Michaelis said of George Wilson, "He was his wife's man and not his own."
Discovering Myrtle's infidelity stunned George and drove him into uncharacteristic behavior. He made her a prisoner, literally locking her up in an upstairs bedroom. Visiting George at the gas station, Michaelis heard "a violent racket" that "broke out overhead." When George explained that he had locked up his wife, Michaelis was shocked:
Michaelis was astonished; they had been neighbors for four years and Wilson had never seemed faintly capable of such a statement.
George locked up Myrtle because he knew she finally had reached a point in their marriage when she would leave him. Despite their years of unhappiness, Myrtle had stayed, but circumstances had changed. George believed Myrtle had somewhere else to go, and he was determined to stop her.
Wilson now knows about his wife's affair. He is enraged, and instead of confronting his issue directly with who did it, he plans on running away from his issues. Fitzgerald reveals interesting characterization here because the reader would expect a different reaction. Simply put, he wants to get his wife away form the temptation, and them as a couple away from the problem.