He doesn't know what to do with that. Steve can't even fathom a version of Howard who would do something like that. He could be insensitive to the feelings of others, but generally he cared. He tried even if he was lousy at thinking things through when it came to people. He can't reconcile what Tony is saying in regards to him with what he knows.
All he can do is focus on the rest of it which just frustrates the Hell out of him. It shows on his face; the growing disbelief that this is his explanation for his behavior. "And you took it out on me or wanted me to take it out on you. I'm honestly having trouble figuring out what you were doing back there other than showing how you little you respect me."
All Steve hears is Tony talking about Tony. It's like nothing he said got through to him. He sighs in exasperation. "Do you see the problem here? You can't say you want to fix us when you basically just admitted the way you acted had nothing to do with me. You don't care about us. You care about you. You don't want me to be angry with you. What I feel means nothing unless it stops you from getting your way. Whatever that is." He can't pretend he knows why Tony is still bothering with him other than it's something to do.