Wow, that is really really tough. The reasoning makes no sense indeed - he could have talked to you about how you both could prevent him from needing to see/talk to that 'S' person - like adults.
My parents recently found back friends they suddenly lost 20 years ago - there were really good reasons for it now they've talked about it. They are now catching up time. I hope something similar happens for you and your friend :-)
That's exactly what I had in mind, making plans for meeting/seeing him somewhere out in the city, neutral place. But unfortunately he rejected my idea and chose not to have any form of contact with me. I am happy for your parents that they were able to reconnect with their friends after 20 years. I hope I won't have to wait that long ...