The speaker is someone who has been rejected, probably by a parent, and who now hurts so much that they turn to self-harm. The line "To make me feel something" suggests numbness: the pain of cutting seems easier to bear than feeling nothing at all. Twice the speaker repeats "Because of you," pinning the blame on the person who left, and the repetition makes it sound like a wound they keep pressing on.
The most revealing moment comes near the end. "Did you forget, / I was you baby girl?" The grammar is slightly off, but the meaning comes through: the speaker was once cherished, or at least once belonged to this person. Being "thrown out" of their world is the final blow, and it explains the loneliness of "Forever." The mood is raw, bleak, and accusing. The short, broken lines feel like someone struggling to get the words out, and the poem ends without comfort or resolution.