Who is Dottor Alessandro Postiglione from The Sixteen Pleasures and what is their importance?

Dottor Alessandro Postiglione first appears on the scene as a stranger who is offering an umbrella and a place to stay to Margot the night that she arrives in Italy. She declines his offer. They meet again on Thanksgiving day and go to a coffee house together. He helps her find a place to stay at the convent where his cousin lives. He helps Margot with the restoration process, which he understands because he himself is an art restorer. She works on the book in his apartment. The two become friends then lovers. In spite of a wide difference in age, they fall in love, and he even contemplates marrying Margot, but he is still having trouble receiving an annulment from his wife who he has been separated from for many years. Although the relationship doesn't work out between the two of them, Margot knows that he truly loved her as much as she loved him.