My girlfriend criticized me so I punched her.
You can't be serious. Why would you do that to your girlfriend?
All the bullshit she had said over the course of our relationship was eating away at me and I exploded
That doesn't give you the right to punch her. That's assault and domestic abuse. You could go to jail for that.
She deserved it.
No one deserves to be assaulted, especially not your girlfriend. If you have an issue with what she's doing then you should talk to her about it.