Self-harm is often a way of coping with painful and difficult feelings and distress. Someone may harm themselves because they feel overwhelmed and don't know how else to deal with things. It's usually a very private issue.
Everyday, I fight back the urge to text you or call you, telling myself that if you wanted to talk to me, you would. Do it anyways, chances are they are sitting there checking their phone every ten minutes to see if they missed your text!