I physically hurt my ex-girlfriend and I don't think I'll ever forgive myself. I just hope she'll be okay.
What made you want to hurt your ex-girlfriend?
I was just so angry and I lashed out before i could think of what i was doing
Experiencing remorse after physically hurting someone is a natural reaction. However, constantly dwelling on your past actions, though they were bad, well lead to depression and emotional harm. You should work with a therapist to process through what happened in your previous relationshipo and to ensure that your anger management skills remain effective.
I'm just going to ignore the pain and pretend it never happened.
That is the wrong way to go about it.   The most important thing is to never do this again.  Get help and find out what made you prone to do this, so that you don't make the same mistake again.