Answer:
The sentences in this excerpt from F. Scott Fitzgerald's "Winter Dreams" 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" and "There was nothing sufficiently pictorial about Irene's grief to stamp itself on his mind"
Step-by-step explanation:
These sentences show how insensitive he is, and how little the feelings of others can affect him, the keywords to define this are "nor, did, regret" and "nothing about Irene's grief to stamp on his mind", these words demonstrate a personality that is unable to empathize with others. He can not create any kind of emotional connection.