Jack is actually kind of surprised by Robert's change as well.
"Hey, why did you tell them to leave? Is it because of that attack?" asks Jack.
"Yeah." Robert looks away. He doesn't want to tell Jack the whole thought process.
It is really because of the attack and the fact Robert thinks he is distracted by Rosanne.
"Well, in that case, are you going back to your apartment? Actually, don't go back to your place. I don't think you should be alone right now. Why don't you come upstairs?" Jack suggests.
Robert laughs, "Ha ha, my gosh, I'm OK. I can take care of myself. I've always had. And I've always been alone."
Jack shakes his head, "Man, don't be alone right now. It's not that I don't trust you can fight off random attackers. Just... come up and have a beer or something. I bought a six pack."
