What should I do?

My boyfriend has had 4 of his closest friends break his trust in the last year or or. They had known each other since elementary school and started college together almost two years ago. This has changed the way he views the world and his ability to trust people drastically. I'm afraid that he's becoming jaded and cynical. How can I help him if that's even possible? It breaks my heart to see such a kind and beautiful person feel like everyone he trusts is someday going to hurt him. I don't know what to do.