Why doesn't Nnaemeka want to write to his father about his marriage plans?

This refers to the story "Marriage is a Private Affair" by Chinua Achebe.

Nnaemeka wants to wait until he can see his father and is able to tell him in person. He is worried that his father will hate the idea of the marriage, because Nene (his fiancé) is not from the Ibo tribe. Moreover, she was not chosen for him in an arranged marriage, as is tradition. Nnaemeka is worried his father will disapprove of the marriage. He ends up being right as the father is enraged to find out the news.