Your fiancÚ, nor anyone, has the right to harm you.
The fact he is taking his anger out on you is unacceptable. If you decide to keep him in your life, you must set limits with him. Speaking to you in an emotionally abusive manner is no longer an option for him.
To be blunt, you need to set limits with your fiancÚ about the behavior you find acceptable and that which is unacceptable. There are consequences for unacceptable behavior. But only set limits and consequences if you are prepared to follow through with them.
These are not punishments, nor are they forms of blackmail. You are telling him, unequivocally, what you will tolerate.
He has every right to be angry, depressed, and rageful. But taking it out on you and others is not an option.
Loving him means setting limits. Hopefully he will see that he has to find constructive, rather than destructive, ways with which to deal with his pain. You are setting limits out of love.
Dealing with this stuff is not easy, not for the survivor, and certainly not for the person who loves him. But it can and does get better. A lot of energy and committment is required to achieve the desired results.
Your fiancÚ has a lot of diffuse rage for which he does not have a specific manner in which, nor a specific target at whom, to express it. His rages and arguments are defenses against the pain he feels. But he needs to express his pain in a manner that is not harmful to you, to himself, or to others.
The truth is, your fiancÚ survived the worst part. While the memories and feelings may be painful and unpleasant, they are just that -- memories and feelings, and they cannot harm him.
This is not to say the feelings, flashbacks and memories do not hurt. At times that pain is excruciating. But using rage and verbal abuse to distance himself from further pain is neither appropriate nor helpful. The only way to get the pain to stop is to do the work in therapy.
It will be a rough road for each of you, but the rewards are immeasurable.
One of the things you need to do is self care
. You need to eat well, exercise and do things that are not trauma related. You need to have a support system that does not focus on trauma related issues.
If you have not found it yet, there is a chat room (aka: the lounge) which includes a room just for friends and family.
The best way to support him is to continue working with your therapist and to be healthy.