The speaker is hurting because of someone close to them, and it seems to be a friend, since the prose lines near the end mention a friend's messages. The central image is tinted glass that has "lost its colour." Everything looks different, and words that once passed as jokes now land as wounds.
The poem is full of questions. The speaker wonders whether they are the problem, whether the other person is, whether the two of them just don't fit, or whether both share the blame. None of these questions gets an answer, which makes the confusion feel real. Still, the speaker believes the "window tinter" will return and that things will look the same as before, though the pain right now is "unbearable."
The final lines are the most honest. The speaker feels they have no right to complain, since this is how the friend has always been. The mood is sad, uncertain, and quietly self-doubting.