After our last fight about sex, I was looking for a book to buy her about PTSD. She called me the next day and said that she went out and purchased PTSD for Dummies. I know there are other suggestions in the book thread by Anthony. Perhaps you could encourage him to educate himself in another way. A website with people with issues he doesn't understand may be a little too daunting for him.
My girlfriends attitude has changed some since she started reading the book.