"Why do I?" is a raw, unfiltered stream of questions from a speaker who feels sad and angry and can't work out why. The poem opens with simple, repeated "Why do I" lines, and that repetition makes it sound like someone going round in circles, unable to find an answer.
What stands out is the fear. The speaker is scared of themselves and of "what I'm capable of doing." They cry, pretend everything is normal, and push their problems down, hoping they'll vanish. Then comes the most painful turn: they wonder whether even their feelings are real, or just an act or excuse to feel better. Underneath that doubt is a harsh belief that they might be "a terrible person."
The mood is anxious, lonely, and self-critical. The broken, unpolished sentences and the line breaks near the end make the thoughts feel like they are tumbling out, unfinished, ending on the same unanswered question.