Les Amants Réguliers

sometimes it seems so easy

Does Bogart call Bacall "Slim" in To Have and Have Not, even though the character´s name is Marie, because you called your wife "Slim" ?
Yes.

And why does Bacall call Bogart "Steve", even though his character´s name is Harry ?
Because my wife called me Steve.

(Howard Hawks: Hawks on Hawks, Joseph McBride)
.