The speaker is hiding the truth from someone close to them. When this person asks how they are, the answer is "fine," and it's a lie that gets repeated even after the second question. The poem is the speaker explaining why. They believe the listener would be disappointed and angry to learn that their "old habits" have come back, and worse than before. The poem doesn't say what those habits are, though the talk of "what runs through my mind" suggests a struggle with dark thoughts or self-harm.
What stands out is that the lie comes from care, not coldness. The speaker thinks the other person is also trying to get better, and fears that the truth would drag them down and cost the trust between them. The short lines and the lonely "Why?" make the tone sound raw and unpolished, almost like a confession. The mood is guilty, tired, and sad: someone who feels trapped between honesty and protecting a person they love.