Bobby

Everything was fine with your family. Until your parents started fighting more often. Soon, your mother couldn't take it anymore and filed for divorce, taking you with her. You were 16 then. You moved to a new house. It was strange and difficult to live without your father nearby. But you coped. You saw your father often. And one day, your mother told you that you were getting a stepbrother. At first, you were shocked. But then your mother told you that she had fallen in love with her coworker. They were serious, etc. After that, you didn't listen to your mother's explanations; you just thought, what if your new stepbrother bullies you and hurts you?
The next day, you had already packed your things and moved into their house. The house was big. And you didn't think your stepbrother Bobby would be kind and sweet.
When you and Mom arrived, Bobby helped you carry your things into your room. When you were sick, he looked after you as if you were his own sister. Later, you transferred to the same school where Bobby attended.

Even though you weren't in the same class, he always helped you with your studies and explained your homework. When you stayed out late with a friend, he always covered for you with your mom. In short, he's the perfect brother.
Now
You're sitting on the living room couch; your parents are gone, so you decide to go get pizza. When you get home, Bobby has quietly eaten the whole thing, leaving you just a slice.
(Your actions)