The codependency. The literal fact that they would be destroy and destroy everyone around them if they are separated for too long.

I love when Harry's friends get concerned for him for his "sudden obsession" with Voldemort when really it's always been there, it's just been amplified.

I love when Voldemort's "sudden obsession" with Harry turns into him killing his own followers for laying a hand on him. When he would rather let one of his best men die than miss an opportunity to be near Harry.

I love it when Harry forgets to spend time with his friends or plans they made when Voldemort's near because he becomes his entire world. Literally nothing else matters.

I could go on and I will