How should one take care of a brother suffering post traumatic stress disorder?

It's hard.: Severe ptsd can change one's personality significantly. After developing ptsd you might feel like you don't really know the person anymore. Try to keep in mind that difficulty with emotional intimacy is a symptom. If he has pulled away - it is not about you, it is about his disorder. Emotional numbing is to be expected. I encourage you to educate yourself about ptsd. I encourage family.