How we cite our quotes:
What a good actor he was. The thought makes me sick to my stomach, because even though I left them too, at least I was no good at pretending. At least they all knew that I wasn't selfless. (6.30)
Tris deals with her brother's secret in a classic, sisterly fashion: by feeling sick to her stomach. It's interesting that what really bothers Tris isn't the betrayal of the family—both kids left, after all. What really bothers her is how good he was at keeping that secret for so long.
"Because I've told them," she says, through the gritted teeth of her smile. Her teeth are straight on top and crooked on the bottom. She looks at me. "We try to be pretty honest about our feelings in Candor. Plenty of people have told me that they don't like me. And plenty of people haven't. Who cares?" (9.24)
In direct contrast to Tris and her secretive family, we have Christina and her crazy truthful Candor ways. Don't like someone? Feel free to tell them. Candor try to live a life of radical honesty—which kind of makes Christina the opposite of Tris in this one area. And also probably makes for some awkward Thanksgivings.
Fear prickles inside me, in my chest and in my head and in my hands. I feel like the word "DIVERGENT" is branded on my forehead, and if he looks at me long enough, he'll be able to read it. But he just lifts his hand from my shoulder and keeps walking. (13.74)
Tris is worried that her secret about being Divergent is pretty obvious to Four. Which is the downside to keeping secrets: you're always worried that someone is going to find out. So here, while Four seems to be supportive, Tris still feels like she can't share her full identity with him.