"Don't waste my time..." and
"You only have yourself to blame..." are horrible indictments of a pair of parents steeped in a culture of "tough-love" neglect. Again, you hold true to the metaphor. The reader understands the "back pain" represents extreme emotional burden, but it is still couched in physical terms. It would have been easy to change over to speaking in emotional terms at this point and abandon the metaphor. The fact that you stayed on target is admirable, indeed.

The strength that is shown as the speaker continues
"to crack my back all by myself" brings hope to the reader. The piece doesn't end with rainbows and unicorns; another good choice, because life is rarely like that. But it doesn't end with surrender and self-destruction, either, which is too
often how hard times end. We are left with the image of a young man bearing up best he can when he has found no one else to help.

The pain of abandonment is intimated, but not harped on; I think that was another good choice. In a lot of writing about personal challenges—mine included—writes can get all wrapped up in the emotion and swamp the reader with smarmy effusiveness or tarry depression. Your choice to demonstrate quiet, grim determination lends further reality to a piece we can already all relate to very well.

By way of constructive criticism, I would observe that this could work better as prose by adding a bit more detail—not too much, but perhaps a line or two—and reducing line breaks to make fuller paragraphs, more complete thoughts. On the other hand, it could be pruned a bit into lives of verse without losing the overall impact. Eliminating articles and shorting phrases would help or rearranging existing wording to offer a rhythmic cadence.