Well done OP for starting to read the book and for leaving your ex-boyfriend.
I can tell you from my own experience, under no circumstances have any kind of contact with him. No matter what he'll ever write to you, don't answer and if he'll show up, don't talk with him and run away. Even if you really want to answer and tell him or explain anything to him, don't do it.
That's how the trap works, at first you think ok, I'll answer and tell him one more time not to contact me anymore. By doing it, he'll carry on contacting you. Somehow, you are drugged again in a conversation with him, even if you intended from the start only to tell him one more time not to contact you. After, you may be dragged on to have a last time meeting and separate amicably. After you are back again with him and you can't even explain to yourself how it happened and why you are again in the same situation with him.
This is one the reasons why it's so hard to separate from them for good and a lot of women go back to them. It's like a continuing loop and the only way to break it, is by not having any kind of contact until he gives up on contacting you. If he continues harassing you, contact the police. Maybe a call from police will wake him up and he'll stop doing it and move on.
Hopefully, he won't contact you anymore and you can move on with your life.