Unfiltered truth all the time? That's just ridiculous. If someone is telling you the truth constantly, there is no trust involved. You don't need to trust that person. If you trust their motives, their heart, then you trust that any lie they tell you won't harm you. Then the only lies that become taboo are the ones that cause issues. ie cheating, something that can eventually cause physical harm, etc. Unfiltered truth is a ridiculous (unattainable) standard for anything.

Deep in your heart you know that you never can.

Suppose you wake up one morning, and your beloved smells of vomit, their hair is mussed, and they look like death warmed-over.

Is honesty called for, here?