I think that on some level you must feel bad or you wouldn't be asking for advice. Also It is pretty unpleasant to have someone sending you nasty messages. So. I would propose this.
Send him one last email. Tell him you can see he is upset by the way he felt he was treated and that you are sorry if he feels that you failed to communicate properly with him.
It appears you don't want to see him again which I get as personally I would run a mile from someone barraging me with texts when the feeling isn't mutual.
So be upfront. Tell him in a nice way that it just didn't click for you, he is a lovely guy but you really don't want to lead him on.
If you do that or something like it then you have no reason to feel that you have been underhand and then hopefully he gets the message and his anger subsides as perhaps he wont feel so used.