Tony:
What he calls you: Baby, angel face
What you call him: babe, sugar
Bucky:
What he calls you: beloved, sweetheart
What you call him: Soldier, Hero
Clint:
What he calls you: kitten, babe
What you call him: Legolas, hun
Thor:
What he calls you: Princess, Poptart
What you call him: gorgeous, Goldilocks
Bruce:
What he calls you: honey, lovely
What you call him: Robbie (you call him this because it's a nickname for his first name, Robert. He hated it at first but grew to tolerate it. It's especially helpful when you're on the phone when people are planning surprises for him so you can tell him in code so that the Other Guy doesn't make an appearance.). You also call him hero and love.
Pietro:
What he calls you: darling, princess
What you call him: zoom, sweetheart
Steve:
What he calls you: darling, love
What you call him: superstar, handsome
Fitz:
What he calls you: honey, mo leannan (it means my love in Gaelic)
What you call him: Leo (it's his name), hun
Sam:
What he calls you: babe, baby, sunshine
What you call him: Sammy, pumpkin