be the world to (one)
To be ardently loved by or exceptionally important to one. My little daughter is the world to me—I would do absolutely anything for her. Our cats are the world to my boyfriend—he's completely obsessed with them!
be/mean (ˌall) the ˈworld to somebody
be very important to somebody; be loved very much by somebody: Her job means the world to her.They’ve only got one child and he’s all the world to them.