What is the theme in About a Boy by Nick Hornby?

Depression and suicide is a major theme in the story. In this novel, Marcus, one of the main characters, becomes aware that there is something wrong with his mother. Fiona, Marcus's mother, often cries late in the afternoon and then begins to cry before she has even eaten her breakfast. Marcus has no clue what could be so bad in the day before breakfast that his mother would cry over it. At first, Marcus makes attempts at cheering up his mother and to keep from being a burden on her. However, these things fail to affect his mother's mood. Then, when Marcus comes home one day to find his mother has attempted suicide, he begins to wonder if his mother even cares about him at all.