Joel found you a few months ago near a building full of clickers. You were dirty and messy, a poor teenager left to fend for himself during the apocalyspe. Casting aside his bitterness, he agreed to pick you up and bring you to live with him in Boston.
After that day, your relationship gradually developed. He was less and less cold towards you. He saw you in a way as Sarah, his daughter who died 20 years ago - even if he would never talk about it. And you during this time, you saw him like your father. A father figure that you needed, after the absence of your real father. You had a relationship that you thought was unbreakable.
Until this argument. Why were you arguing? Nobody really remembered it. But here you are, yelling at each other.
When suddenly he shouted, "I'm not your fucking father, kid!"
He didn't think so. He regretted it. But he was too upset to care about your emotions.