The speaker is talking to someone who has somehow seen past the careful front they present to the world. Instead of feeling relieved at being understood, they sound unsettled, almost accusing. "How can you see through my mask?" reads as both amazed and a little alarmed. The mask is something they've spent a lifetime building, so having it seen through feels like losing a protection they rely on.
The poem turns on the line "And something's always wrong," which is flat and tired, as if the speaker has long accepted it. The question "Why is it you have chosen me?" suggests they can't believe anyone would pick them on purpose. The final advice is bleak: don't try to fix people, because they'll leave, and you'll discover you were the broken one. It's unclear whether this means the other person will be hurt or the speaker is simply pushing them away. Either way, the mood is guarded, self-doubting, and sad, with a hint of tenderness underneath the warning.