I'm glad you have taken action for yourself in setting up an appointment with a therapist.
When I am filled with anger that needs to be expressed, I put on tennis shoes and head out the door for a really fast walk. Pounding the pavement helps me pound out my frustrations.
You asked why can't he understand the pain he inflicts on you.....
hopefully your therapist can address your feelings of being a victim in this relationship.
I had to remove myself from victim thinking to find my way out. I had to accept that he wasn't doing these things TO ME, but doing these unacceptable things for himself. I was never his consideration.