Outside, Natasha spots Rob and Kelly and watches them. She knows that Rob is surely explaining to Kelly that he's not actually disloyal. Natasha and Rob sat next to each other in AP Physics and after she helped him pass a quiz, he asked her out. Natasha muses that she liked being a couple, and she did like Rob. She'd felt ashamed when he cheated, but she never understood why he didn't just break up with her. Despite that, Natasha got over him quickly, which concerns her. She wonders how she can trust something that seems to end as quickly as it begins.
Even though Natasha had an intimate relationship with Rob, she still believes that she was relatively alone and isolated within that relationship. This could be the case for a number of reasons, but it does begin to illustrate that Natasha isn't keen to trust people with her private self, and it's very possible that she purposefully keeps parts of her hidden that keep her from truly connecting.