It sounds to me as though this man is in the throes of an unconscious inhibition. What this means in lay terms (no pun intended) is that his unconscious mind may be putting up a defense mechanism by inhibiting his sexual response.
As I've explained in other columns, defense mechanisms are designed to protect the self against danger of one sort or another. It is very likely that this man is terrified by the intensity of your connection. He said himself it's the best sex he's ever had. I suspect that it's so good that it's scary to him. So, his mind is actually taking the edge off of the greatness, by not allowing him to ejaculate in this century if at all.
He needs to examine what is scary to him about a connection this good. He will soon discover that he is afraid of 'it' being taken away through death or abandonment. By holding back, his mind hopes to protect him from the pain when the relationship is taken from him. He has a script in his head and he knows the ending already. The script and its tragic ending that he expects is a repeat performance of whatever terrible trauma he suffered during his formative years. Perhaps his mother or father left him outright or perhaps they removed (or threatened to remove) their love from him. He needs to fill in the blanks, and then he needs to be helped to see that his past doesn't equal his future.
You aren't his parent and you don't plan to reject him (not of course unless he succeeds in driving you away through this funky sex business). When he stops bracing for the disaster, he should be able to let go and stop protecting himself. Your support and reassurances that you are not going anywhere can do a lot to help him.
If after all your reassurances, he still finds himself stuck in neutral, he may need a therapist who understands how to conduct a defense analysis in order to help him get over the hump.