The Bat understood that Iris had every night to be upset. There were trying circumstances even for the best of them, and she had a child to take care of; a child whose parents had been replaced by fictional characters, neither of whom had any experience with children to speak of. His empathy, however, only went so far, and his eyes narrowed behind the cowl when Iris told him to take that with him. Selina may have been troublesome, but she didn't deserve to be spoken to as such, and he thought it best that he put as much distance between her and Iris as possible in a short amount of time.
As usual, of course, Selina reacted without thinking. He intended on escorting her out of the apartment, which involved falling into step just behind her shoulder in order to ensure she kept in line, but her movements were swift and he admittedly hadn't been expecting her to go as far as to kick down the door.
"Selina!" The Bat's voice was a thunderous roar, but the armor that had saved his life on numerous occasions also slowed him down, and he entered the room just as Selina flung herself on top of Iris while Gus wailed from behind Finch, who clearly hadn't forgotten the backhand he'd received earlier. The dog swung around, snarling like something wild rather than a domestic pet, and he knew getting past the creature would require methods he wasn't willing to utilize in front of the child. That didn't mean he couldn't get past, however, but before he could force his way past and physically separate the two women Selina had disappeared over the edge of the balcony and into the night.
He opted to leap over the dog in order to reach the balcony, but while the Bat did look down onto the streets below he chose not to follow. Any number of threats from Gotham could be in Las Vegas right now, and he needed to prioritize; he didn't have the time to waste chasing Selina down. If she got into any serious trouble, then he would find her, but for now he let her go.
Gus' cries had faded to whimpers, and the Bat turned to look at the boy, now little more than an overlarge shadow out on the balcony. "You shouldn't have seen that," he told the child, though he was likely too young to understand, before turning his attention to Iris. His gaze was concerned, but Finch was still snarling and it was clear that he would not be allowed to get close to either her or the boy. The message, leave, was clear enough, and even the Bat agreed that he had overstayed his welcome.
"I'm sorry." That was for Iris, and was more a glimmer of the Bruce she'd spoken to than the cold, inhuman Bat that had appeared in Gus' room like a vengeful shadow. "Keep him safe," he added, and with that the Bat hauled himself onto the balcony's edge and, a second later, dropped out of sight.