Cheesy yes I know
Michael:
His: Rainbow, Mikey, Mr. I-do-what-i-want-I'm-punk-rock
Yours: babe, love

Calum:
His: puppy, Cal, Babe
Yours: Beautiful, baby, Marshmallow (don't ask)

Luke:
His: penguin, Lukey, Prince Charming
Yours: princess, baby girl

Ashton:
His: Ash, baby , giggles,
Yours: sunshine, sweetheart