Which sentences in this excerpt from f. scott fitzgerald's "winter dreams" reflect dexter’s heartlessness?
it was strange that neither when it was over nor a long time afterward did he regret that night. looking at it from the perspective of ten years, the fact that judy's flare for him endured just one month seemed of little importance. nor did it matter that by his yielding he subjected himself to a deeper agony in the end and gave serious hurt to irene scheerer and to irene's parents, who had befriended him. there was nothing sufficiently pictorial about irene's grief to stamp itself on his mind.

Answer:

These two sentences show how heartless the character being described is. The author tells us that Dexter did not feel any regret for the night when he acted badly, even after the night was over, or after many years had passed. Moreover, the author also tells us that, while he caused Irene much suffering, her pain was never important enough for him to notice it or remember it.

I believe the sentences that reflect Dexter's heartlessness are:

It was strange that neither when it was over nor a long time afterward did he regret that night.

Nor did it matter that by his yielding he subjected himself to a deeper agony in the end and gave serious hurt to Irene Scheerer and to Irene's parents, who had befriended him.

There was nothing sufficiently pictorial about Irene's grief to stamp itself on his mind.

Explanation:

The main character in Fitzgerald's short story "Winter Dreams" is Dexter Green, a middle-class boy, who grows up to be successful in business and be a part of the upper class. When he is only fourteen years old, Dexter realizes what he truly wants in life when he watches an eleven-year-old and very rich girl having a tantrum. He quits his job as a caddie, plans out his life, and decides he wants that girl, Judy. There is something about her spoiled behavior that attracts Dexter's narcissistic personality.

Around ten years later, they meet again and become romantically involved. Judy, however, is nothing but superficial. She wants to be admired, and is constantly bored by her easy, problem-free life. So she keeps a dozen men around her, constantly feeding them some hope, only to withdraw it in a matter of days and trade them for a new man. Dexter decides he is tired of being her toy. He gets engaged to Irene but, as soon as Judy shows interest in him again, his fascination for her overwhelms him. He breaks off his engagement for her.

The excerpt we are analyzing here shows how heartless and incapable of empathy Dexter is. Judy is his ideal. She represents his dream of wealth and power. He leaves the possibility of true love to have Judy for just a month, since she gets bored and tired of him yet again. Still, he does not regret doing it at all. He'd much rather have Judy for a month than keep his word and marry Irene. Irene's feelings, her parents' opinion, popular talk, none of them has any power over him. He must have what he wants, and he does so cold-heartedly. From the excerpt, the sentences that best show these traits are:

It was strange that neither when it was over nor a long time afterward did he regret that night.

Nor did it matter that by his yielding he subjected himself to a deeper agony in the end and gave serious hurt to Irene Scheerer and to Irene's parents, who had befriended him.

There was nothing sufficiently pictorial about Irene's grief to stamp itself on his mind.

sentence lenght varies according to word choice.you select which word to use and that will require to use other expressions that collocate with the word chosen.sentence length will vary   according to the choice of words you make to express your ideas.