At first Steve looks at him like he's crazy. He's so insistent that he finds himself caving. It honestly can't hurt at this point to go long with the crazy billionaire. It's when Tony doubles down that Steve shrinks a little in his embrace like a frightened animal who doesn't know what to make of affection.
Slowly, but surely he starts to relax. Against his better judgment, he asks the questions that have been plaguing him since meeting Zola. "Do you think my life is worth anything? Did I die for nothing?" This isn't outright self-depreciating. He truly wants to know as sad and terrible as that is. He honestly doesn't know if he has any value to their world anymore.