Have you ever learned any coping skills to replace the self injury behavior?

I know how you feel. I sometimes have those bad thoughts too. Here is some of my coping tools. Read a good book or talk to somebody who you trust. Wanting to end it all will not solve anything.

I've been in a similar situation and although I will not understand each of your struggles completely, I know how it feels to remain clean for months and maybe even years, however, falling back into the same habits. My suggestion to you is take a deep breath, listen to music, read, walk around the neighborhood, pet dogs and cats and horses and cute lil hedgehogs, or look at some cliche beach pictures on tumblr.
Why:
Listening to music increases dopamine levels by ten percent. If you're an introvert, reading is a great strategy to calm down and recharge. Walking releases healthy chemicals such as serotonin (just a small side note, chemicals released while walking and listening to music are almost the same as self-harming. The only difference is that it's healthier and less concentrated if one were to receive these "feel good" chemicals through exercise and music than self-harming or alcohol). Petting cute lil animals has been proven to lower stress levels. And... cliche beach pictures are just really pretty to look at and may help divert your attention elsewhere.