"I don't love you."

Those words ache him even though he said them himself. Seven wants to be with you, truly. But he cannot allow you to get hurt due to his dangerous job as a hacker. People can use you as an advantage. As a weakness for him. He can't afford that.

Seven is pushing you away when all he really wants to do is hold you close. He made a promise to distance himself. He wants a happy ending with you. But with him? Happy endings are always going to be nothing but a mere dream.