Missy, I can tell you from experience, there are drugs that do help and his reaction is "normal". That said, it doesn't make it easy on you.
When my husband was given the diagnosis that the radiation was infiltrating his good brain cells and would eventually kill him, his personality changed. He had been a loving and compassionate man, who never lost his temper and respected me and my abilities. He never in 38 years of marriage raised his voice at me or our son, but always argued his point with logic and respect. When he got the Dx he became angry and upset - down right ugly and mean to me when we were alone and when others were around he sang my praises to them. He had never been critical of others and not self-centered. And now he criticized me constantly and felt he was the only one scared and angry.
One day at a doctor's appointment I mentioned, in front of Ron, the change in personality, and the doc talked to him and suggested we see a psychiatrist for counseling for both of us. (I should insert here,that my husband was a psychologist and should have recognized the need, but didn't.) He agreed to the referral when the doc said it would be good for me. The first appointment and Dr. Reinke suggested a med for my husband to help with his anxiety and Ron agreed to give it a try (for me). It took awhile to get the right dosage but once we found it things were easier for both of us.
My husband lived two years from the DX and we had some good talks and I have good memories erasing the hurt and abuse that was present before the meds.
I've been in your shoes so if I can help by listening - please PM me anytime. Now I am in your PALS shoes and know how cheated he feels and how angry it makes him to have to watch you do what he used to do. My husband said it was humiliating to have me take over his personal care and we talked about it after he was more rational and he understood I did it out of love.
One funny story - one day he broke his glasses by falling on them when we were running late for a doc appointment. I told him we would go by the optomitrist office while in town. He said he had his old pair in the top dresser drawer and I should get it out. Well, I opened the drawer and found every pair of glasses he ever had! I mumbled something about why in the world anyone would keep all the old glasses. His reply "Well, the next time I die I will remember to leave things better organized for you." Wow - the impact that had - he wasn't planning on this at the age of 57 and neither was I!
Hugs and prayers,
Diane in SD