Matty Forever by Elizabeth Fensham

Bill and Matty are neighbours. And best friends. Together they share their deepest, darkest secrets and lean on each other when things aren't right at home.

Bill is missing his father and having a hard time at his new school. And Matty is realising that her family is not quite the same as everyone else's.

But when new girl Isabella decides she wants Bill all to herself, Bill and Matty discover what true friendship means. -Goodreads