From my experience, being woken up is usually a very good thing. For one thing as his significant other, you will be a heck of a lot better to see than whatever is going on in the nightmare.
If the trauma he experiences in the dream is still bothering him after waking him up, try reminding him to breathe deeply to re-ground himself in the present.
I have heard dream rewriting has worked for some. I have also done some dream control exercises in the past. If you would like details on these, feel free to PM me.
The nightmares are a symptom, not a problem. They too shall pass as the problem [abuse] is appropriately dealt with and processed. I don't know how long this will take, its different for every survivor.
All the best,