Granted being an AI Cortana couldn't really "love" anyone, right? But throughout the books and games we see time and time again Cortana has a slightly unnatural attraction and devotion to John, even demoting the Colonel who rigged John's training test. She seems to protect him more than she would anyone else. Of course it's perfectly possible she just really liked him, but even whilst aboard [i]High Charity[/i], it is said the thought of Master Chief may have kept her sane. And she continually tries to make physical contact with Master Chief while in cryo-sleep. Granted she was slipping into rampancy (possibly), but still? Just a thought.