People in a long-term relationship develop bonds of friendship and comfort along with romantic feelings. His statement that he hated you was most likely his way of cutting all romantic ties with you, but friendship and comfort is harder to eliminate.
Why does it matter if he is dating someone else or not? Are you interested in getting back together with him? Because, if so, that is probably not the best idea given your history together.
However, if you are comfortable with friendship, continue with the emails and be glad that you have someone in your life who cares.
Good luck.
Brought to you by Dating With Devon!