To add to what Anthony was saying, we let ourselves get close to other people in the past. Too many of them died and left us feeling empty inside. He probably keeps distant with his family because he remembers the feeling of loss well enough that he winds up in avoidance of letting his feelings open up and maybe have to deal with that kind of hurt again. Either way, the impact would be the same because he Loves his family even if he cannot find the way to express it. His mind tells him if he doesn't get close, nothing bad will happen to you. From personal experience, I'd say, even if he won't admit it, it bothers him way more than anyone else in your family, because he knows that he is the reason he can't get close like he would like to. To me, that is one of the worst symptoms of PTSD, people who don't understand eventually go away, and many times we sit there lonely, sometimes for the remainder of our lives, wanting to Love and be Loved, but incapable of changing it, for fear of someone getting hurt because we chose to get close. Aquaintances are a different story, we can be buddy buddy with them, up to a point. When we start caring for someone, the shields go up, to protect both of us. I know this is probably of no comfort to you, except that his distance is a pretty good indicator of how much you are Loved by him. When people say they are envious of me because I don't work and the government gives me a check each month, I tell them, "I'll gladly swap lives and incomes with you, as long as I get to live in your mind and you take over mine". The people who know me never say another word about how I got it made. I hope this has helped you understand that he's not cold, just sick.
Respectfully,
WarHippy1%
PS: '66 and '67 were very bad years to be in-country, be happy that he survived it.