Steve tries to apologize to Tony for all the hurt he has caused since that day with Bucky. Tony tries to tell him he doesn't want to do this right now, but when has Steve ever listened? The emotional unloading that follows and verbal attacks meant to kill, not wound, are just to be expected at that point. Or, Tony has a very emotional response to Steve trying to apologize and lays into him with the force of all the emotional pain he has endured because Steve deserves to feel the pain he caused, right?