I already understand where my mental issues are coming from and I'm healing from it, but I just can't forget those blades I could use for some relief, why? I see them as a way to "express myself" but I have no idea where this is coming from.
There is a high chance you suffer from PTSD, but this you probably already know.
This is not to be taken lightly.
I am not an expert but part of what I relate is based on my own experience, and some studies.
Self-harm is a consequence of self-hate. Complex-PTSD people may have more than one "self"; while the main self takes car of daily life like a normal person, in background (I mean unconsciously) there may be more than one sub-self, able to think autonomously to a certain degree, mostly emotional, that is ignored by the main self to keep on living.
One of them may have buillt and intense hate towards "you" (every self here is you, indeed) - you feel relief because this part feels accomplished by having expressed self hate with a damaging action.
I think finding the buried reasons of self-hate may help to reduce this. Self hypnosis, internal dialogue, or simply a Munka extended meditaton to get rid of self-hate may help. This may take months depending on severity of the issue. If you are already healing yourself probably you are already aware of this.