What is the definition of really knowing someone? Do you have to know all the details of a person's life to truly know them?

For me that's a complicated answers which I don't feel like anaylizing right now as it would way to long of a post.

But I feel I do know my T, in essence/spirit? I do love her and care about her. She does irritate me, upset me, and frustrate me sometimes. She also makes me feel comforted, safe, and even can make me laugh. She has feelings too. It's not fake. Sure some of it is me reflecting? onto her, but I am still able to see her as her own person.