Cass always felt so much more comfortable around Connor then any other human being. With the Elite, she was constantly being evaluated on her physical talents, what she brought to the table. Bruce was testing her on whether she was becoming a better fighter, a better acrobat, a better detective, a better Bat. Barbara, who'd been like a mother to her, was always worrying about whether or not she was becoming the kind of person Barbara wished for her to be.
Cassandra was fine with all this. It was what she was to everyone but herself; a thing. A hammer, a nail, a saw, but never a carpenter. She wasn't a person to these people. She was an ally to some, a tool to others, a daughter to Barbara, but never a person.
They all denied it, but Cassandra saw the truth. She saw from the way Oliver stared at her he was thinking about her in a way she didn't like, she saw from Batman's shift in posture that he was thinking she was regressing in talent, she saw from Barbara's slightly upturned lip that what she was doing was furthering her down the path of a superhero and not that of a human.
With Connor, he was smiling at her. No matter what she did, Cassandra saw him accepting her, both on the outside where everyone could know, and on the inside, the part that only she saw. Whether or not Cassandra walked into his house feet-first or fist-first, he'd respond appropriately. Connor never thought of her in the way Ollie did. Connor never made her feel ashamed of her for developing talents and skills in the way Bruce did. Connor never discouraged her from her life choices in the way Barbara did. Connor loved her, for who she was.
Cassandra was never going to let him down.