How to help him get over it?

Today my boyfriend told me about his best friend, seemed he knew his best friend's death, which we hided from him for nearly two years, he told me he was not mad at me for not telling him as he knew I was afraid he would leave me if he knew it and knowing why his friends did not tell him as they worried he would go crazy and the whole company he set up would be in a mess. He told me not to tell his friends that he knew it, my guess would be he did not want everyone worry about him or panic. Now I was quiet as I did not know whether he was testing his thought on me or he really knew it, also I know the best way could be let him alone, give him some space, and comfort him, but since now I am not sure whether he really knows it or not, what should I do now? And how can I help him to get over it? His friend is his soul, is his half life as he said, nobody can replace his friend's role in his heart. Much appreciated any suggestions.