Pre-covid I volunteered with a charity (not in Hull unfortunately) which provided support to people suffering loneliness via meetings, phone calls, drop-in sessions etc. What I learned from that is that contact is important and valuable but it mustn't become oppressive for the receiver or too demanding for the giver. In your shoes I think I'd arrange to call the chap at arranged times, that way he can be prepared for it, or he can choose not to answer. It's also ok to ask him if he wants you to call at all. But do consider what it means to you, it's unlikely to be easy. You might be taking on a responsibility you ultimately don't want or you might find it all a bit stressful if the chap never responds or engages with you, or if he starts to become dependent on you. Good luck.