I would say someone becomes an "addict" when they are constantly turning to self-injury instead of choosing some other method of releasing emotional stresses. When you cut, for example, a few time a year, I would say your not an addict; but if you cut maybe once a month or more I would consider that an addiction. It just depends on how much you do it in any given period of time and where you are emotionally when you self-harm, and why you self-harm.