Someone trusts the speaker enough to share their secrets, and the speaker can only answer with lies. That's the whole poem, but the two short lines carry a lot of weight. The imbalance is the point: one person opens up, the other stays closed.
The speaker seems to feel guilt, and maybe shame. There's no explanation for why they lie. Is it fear, or an inability to be vulnerable? The poem doesn't say, and that silence makes it feel more honest. The word "all" suggests the speaker wishes they could do better but can't seem to manage it.
The title, "Whitewash," adds another layer. To whitewash is to paint over something so it looks clean, or to cover up the truth. The speaker's lies work like that: a smooth surface hiding what's underneath. The mood is quiet, regretful and a little cold, like a confession the speaker makes only to us, not to the person who deserved it.