Answer:
1.
Gatsby ends his partying lifestyle so completely and so suddenly because he has lost the love of his life, Daisy Buchanan, and the social status and wealth that he has worked so hard to attain.
Gatsby's "career as Trimalchio," a reference to the character in the ancient Roman satire "The Satyricon," symbolizes his lifestyle of extravagance and excess. Trimalchio is known for throwing lavish and opulent banquets, and Gatsby's parties are modeled after these banquets, with endless supplies of food and drink, and entertainment provided by musicians and performers.
Gatsby's partying lifestyle is an important part of his identity and his pursuit of wealth and social status, and he is devastated when he loses both Daisy and his social standing. This leads him to end his partying lifestyle so suddenly and so completely, as he no longer has the motivation or the means to maintain it.
2.
Tom and Gatsby engage in a battle for Daisy's love in the hotel parlor. Ultimately, Tom wins this battle, as he is able to use his wealth, social status, and physical strength to assert his dominance over Gatsby and maintain his hold on Daisy.
Throughout the novel, Tom is portrayed as a wealthy and powerful figure who is used to getting what he wants, and he is determined to keep Daisy by his side. He is physically and emotionally abusive towards Daisy, and he is jealous and possessive of her. He is also threatened by Gatsby's wealth and success, and he sees Gatsby as a rival for Daisy's affections.
In the hotel parlor scene, Tom confronts Gatsby and demands to know the truth about his relationship with Daisy. Gatsby admits that he and Daisy have been in love, but Tom is unconvinced and continues to belittle and humiliate Gatsby. He also reveals that he has evidence that Gatsby is involved in illegal activities, and he uses this information to further undermine Gatsby's credibility and reputation.
In the end, Tom is able to assert his dominance over Gatsby and maintain his hold on Daisy, as Daisy is unable to stand up to Tom's abuse and manipulation, and she ultimately decides to stay with him. Gatsby is left heartbroken and defeated, and he is unable to win Daisy's love.