Idk what to do

I have this friend whom I consider to be my best friend. I doubt she feels the same way but we are definitely close. I do not tell people things and I keep everything bottled inside, yet she is honest with me. i know she doesn't tell me everything, but she is honest with me, and so, should I be honest back? (I don't exactly lie, I just say im ok when im not, and I lie to protect others feelings, but should I be more transparent?) After all, she is the closest thing to a Best Friend Ive ever had.