Carl was your best friend since the prison,along the way he slowly started realizing how much you reminded him of Sophia.

your way of acting even you attitude reminded him of her,that mad him realize he still didn't get over her death.

you finally made it to Alexandria when on a random night he decided to tell you about Sophia, how much you reminded him of her...

"I thought I was over her,but when I look at you I just..."

he sighs

"see her in the back of my mind all the time"