Secondly, the next day he gave me a "dear john" email saying that we were not on the same paths.
Hi Lucy, I think the answer to your question lies in something you said in your letter.
Unless your date was only looking for the occasional social companion, or just someone to become good friends with, he probably sensed that this would not become anything more than platonic.
As shocked as you might have been, it seems to me that he did you both a favour by ending it and moving on before someone got hurt.
You need to start now to find someone special, or perhaps consider dating younger men.