I am somewhat convinced that if a particular person leaves my life, then he will not be hurting my family or me any more. Am I correct in thinking this way, or should I forgive anyway?
Forgiveness need not be reserved only for the times in which you feel deep resentment which might be making you miserable. At times, you might want to forgive simply because forgiveness is centered in goodness because it is a moral virtue. In this latter case, you are forgiving because forgiveness is an end in and of itself. Regarding this issue of deep resentment, it can stay with us even when people physically move away from us. They still remain in the heart and the heart can be restless until the offended person forgives. So, even if the one who hurt you leaves, you can forgive because: a) forgiveness is good in and of itself and b) you might still be resentful and want to be free of that.
For additional information, see Do I Have to Reconcile with the Other When I Forgive?