见外 To see as outside. To treat someone not as a close person but with the politeness shown to a stranger. A dictionary example reads: 我一向把心腹待你，你不要见外. “I have always treated you as a confidant. Do not treat me as an outsider.”
交心 To exchange hearts. To say what is on one’s mind without holding anything back.
心里话 Words from inside the heart. One’s innermost thoughts and feelings.