Both unilateral and bilateral contracts are enforceable in court. For example, a unilateral contract is enforceable when someone chooses to begin fulfilling the act demanded by the promisor. A bilateral contract is enforceable from the get-go; both parties are bound the promise.
Yes, scratching is a form of self harm. Try to tackle this problem while you can because it has the potential to get worse. I started out scratching and now I burn myself with a lighter and cut myself. It's a self-destructive way to deal with overwhelming mental/emotional pain.
In reality self-harm doesn't happen to one type of person, it can't be predicted and scarily, we don't really know how many people are going through it. This is all really vague, but you can take one thing away from it-you are not alone, whether you are harming or seeing someone you love or work with go though it.