形影相追　

◎ 形影相追 xíngyǐng-xiāngzhuī

[never leave each other,as body and shadow comforting each other] 像影子离不开形体一样,一刻也不分离。形容彼此关系密切

形影相追高翥鸟,心肠并断北飞船。——唐· 张说《同张侍御望归舟》