It's like forgiveness. I believe we forgive for ourselves so we can let it go. It only harms us to be unforgiving. I see therapy like that. No one around me may change (and often they didn't) but I have the power to change myself, my responses, how I perceive the situation. Remember, not every thought you have is the truth, much is conditioning. If you have a good therapist, he/she will let you know when you have 'faulty' thinking and you can then open up to a new way of thinking, a new way of perceiving the exact same situation, only from a different set of eyes. You'd be surprised how much that can shift your life.
Often what we believe to be the truth is simply stuff we've heard over and over again, not necessarily the truth or even good for us. Therapy has helped me to sort through those old beliefs and make different choices. Like Pasa said, you''ll get out of it what you put into it.
Your husband and son may continue being who they are now......but you can change, you can make different choices and open up to new options.