What is a character analysis of Charlie Hartz in "The Man Who Jumped into the Water"?

In Laurie Colwin's "The Man Who Jumped into the Water," the reader is presented with the mystery of a suicide.
Through the narrator, Martha, we learn that other people responded to some quality in Charlie that made them want to be around him.

Charlie got the best out of what you were at the time you were it.

Because the narrator was a teenager at that time, however, and she sometimes mentions that her father saw things differently, we suspect that quality often remained hidden from adults.
Charlie also, she tells us, was fully engaged in life: he "put himself entirely into what he was doing." One of those things was diving, and the "water" of the title is the swimming pool that he had installed in his backyard, where Martha and her boyfriend, Jeremy, were hanging out the summer Charlie died. While Martha helped Charlie's daughter swim, Charlie was busy diving, often with Martha's college-age sister. He kept at the diving in a determined way. Another hobby was tinkering with a little car.
Charlie's help in easing Martha and Jeremy's romance is notable not only for her appreciation of his actions but for what it shows about his attitude toward society. The kind of advice he gave, with an apparently off-handed honesty, was the kind "that generally goes over well with adolescents." He arranged for the two of them to have the run of his home while he and his family were away.
As a surrogate parent figure, he advises Martha's sister about her love life and helps Jeremy decide to stay in college. He also encourages Martha to improve her drawing and her backstroke and encourages Jeremy in his photography.
The news of Charlie's death has no buildup. We know everything about him through Martha's filter. Her sister and mother tell her that Charlie shot himself in his car.
The explanations, or lack of them, Martha mostly overhears, such as that he left no note. She and Jeremy are left to imagine—as is the reader—all the missing pieces that would account for his action. The analysis of Charlie that we create is always viewed through Martha's lens, as the first person she ever knew who died.