Bruce really likes Bucky, in a kind of distant, approving way. idk I think I've written it out pretty explicitly in his tags when it's come up, but Bruce feels at ease having someone else be paranoid and disinterested in opening up. They sort of communicate in subtle gestures (doing favors for each other, saying they don't need to owe each other anything, etc.) and Bruce is happy with that. It reads loud and clear to him, and he doesn't need it made more explicit.

This feeling of lack of pressure lead to him feeling pretty open about explaining the Hulk to him. It's nice having someone uninvolved take him completely seriously, but not be scared of him. Just understandably wary. Which is what he should be. Bucky's immediate practical acceptance is Bruce's favorite response of all he gets about the Hulk, because it's a big relief.

Although he's not showing it and is treating him completely like an adult, Bruce is slightly conscientious of how young he is, and is kind of protective. If he was in trouble then the Hulk would probably tear that shit up. :|b