The fact that Tony made sure to reach out to Bruce and help him in a hard time. Just so that there’d be at least once person checking in on him, making sure he’s okay, cutting through the loneliness, even if just a little. The fact that Tony did so even though he himself would have been going through a hard time, and that may have even been the very thing that prompted him to reach out. Being aware of his own struggle may have made him think of a friend who might have been struggling, too. And Tony knows that he would want a friend in a hard time, so maybe he decided he’d make sure to be that for Bruce. But also the fact that he trusts this to not be a one-way thing, and he trusts that Bruce will naturally be a friend to him in a time of need, too. So he shows up for Bruce, helps him build a facility, gives him some company, but at the same time Bruce shows up for him, and lets Tony rant about whatever’s on his mind. Like. They. Carved. Their. Initials. Into. The. Bar.