Keep some doors closed even when you trust the person knocking.

Trust is not a reason to remove every limit. Some things stay private not because you doubt someone but because they are yours, and a relationship does not become more genuine by containing no boundaries at all. Doors kept closed are part of being a separate person rather than a sign of distance. Openness without limit is not intimacy, it is dissolution.

Notice whether you feel obliged to share something because it was asked for rather than because you want to. Keeping something back is allowed and does not require justification. Trustworthy people are not injured by a boundary.