Hi Diannalee!
Welcome to the forum!
His therapist's reasoning sounds really odd to me. Has the therapist ever met you? It sounds as if you both could use some couples therapy with a therapist trained in trauma work.
Your boyfriend's verbal abuse is not acceptable. If you allow him to do this to you, because you feel sorry for him, want to support him, the abuse will only get worse over time. The kind and sweet periods that keep you attracted and hooked into him, become briefer. It can escalate to other forms of abuse. Any form of abuse is unacceptable.
I have PTSD, and no matter what trauma I have experienced, that would never give me the excuse or right to abuse any other living being. He's fully capable of choosing to be a decent, non-abusive person.
Abuse sucks the life out of you. You may be strong now, but being abused drains all the energy and joy out of life. Please don't fall into the trap of thinking that because he is sweet at times in the way that you love, that he will suddenly see the light, become that way all the time, and life with him will be beautiful all the time.
Please learn everything you can about abusive behavior, what constitutes the different kinds of abuse, it's impact on you, how it escalates over time,...
Please don't be in love with the fantasy of who you know he could be. The reality of living with an abusive person is dangerous and life-stealing.
You don't owe him your life, health, hope, dreams in gratitude for his military service.
You do not have to prove you are nothing like his wife. He knows that.
Your promising to stand by him, no matter how badly he treats you, gives him absolutely no incentive to treat you kindly, lovingly with the respect and gentleness you deserve. You have no protection, no boundaries set on his behavior toward you. That does not make for a good, healthy relationship. If one of the partners is abusive, then this lack of self-protection on your part is very worrisome. You are worth being safe, protected, happy...
You are a wonderful person, and you need lots of support and counsel. :hug: