I'm glad he opened up to you. That is a big step in the right direction. I'm going to share something with you that might help you to help him while he's waiting for therapy.
The following flashback halting protocol can be taught. It is based on the principles of dual awareness, reconciling the experiencing self with the observing self. It usually will stop a traumatic flashback quite quickly.
Fill in the blanks:
Right now (you) I (are) am feeling _________________
(insert name of the current emotions, usually fear)
And (you) I (are) am sensing In (your) my body ____________________
(describe your current bodily sensations – name at least three)
Because (you) I (are) am remembering _______________________
(name the trauma by title only – no details)
At the same time. (you) I (are) am looking around where (you) I (are) am right now in _______________
(the actual current year)
Here _______________
(name the place where you are)
And (you) I can see ______________________
(describe some of the things that you see right now, in this place)
And so (you) I know _____________________
(name the trauma, by title only, again)
Is not happening now/anymore.
Print this out and keep a copy so you can help if the need arises.
I know talking to you about it means that the memories are uppermost in his mind. I know what that can do to you and him. I have memories of death and all that goes with it. Not just once, but more than once. He needs a way to release those thought as quickly as possible, so they don't haunt him.
After he gets a good therapist, they will teach him grounding techniques. If they don't, you tell them to do that for him. Also, be sure he is breathing when he talks to you about these things. If you see his head go down, and he is rather spacy, remind him to take some slow, deep breathes, hold it a second, then push the air back out. Long and deep. Have him do that several times. Remember, have him do it slowly or he will hyperventilate. It will calm him. You might even want to do this yourself so you can show him how to do it. Have him look up, into your eyes, and smile at him.
Take care.