How to help someone who suffers from Post Traumatic Stress?

My boyfriend broke up with me after 4 years over a long distance relationship of 2 months. The loneliness triggered his past abusive family relationships and his difficult childhood. He is having mood swings from anger to crying and feeling alone. He doesn’t have many friends in the country and breaks ties with his family. I think he is in therapy atm (PTSD). I felt his anger, disappointment and desperation, he was calling me names. I didn’t respond. A week after he mentioned me by my nickname in his anonymous posts (he told me the website in case I want to follow up on him), where he deals with his past. I ensured him if there is anything I’m there for him. I feel helpless. I still have strong feelings for him, it hurts me to hear he is in so much pain. I’m trying to stay away from this website to protect myself, the break up also wasn’t easy for me.
How can I understand his behaviour, does he need time? Space? What is my role in it? How can I support him? PTSD and borderline is a new subject to me. Thank you.