Zsadist-what he went through at the hands of the mistress was horrible. The sexual abuse he went through is unbearable and was very hard to read. Even though he is "fictional" person...it was still very hard to read what he endured.
His life before his change was that of a slave, but he was a happy slave, it was only after he changed that his life turned to torture. The one person who tried to show him kindness the mistress had her killed. I think that Zsadist gave up hope. He gave up.. When Phury found him and save him "physically" he still didn't have hope. He was a shell of a man. The only emotion he had left was anger and only through pain was he able to live. Remember when he had Phury beat him. That part really did floor me.
Then he finds Bella. He knows what she must be going through beening held against your will. He had empathy for her and he didn't know what to do with all the emotions that brought.
I think that it was hard for him to cope because in his life he was happy and life was ok, then he was a blood and sexual slave and then life was ok. I think what was so hard for him was living in fear that the "bubble was going to burst"
Zarek-His life was nothing but pain and torture. Never in his life did anyone show him any love and compassion.
Even though he still had a heart in him. I think about how he went to his mother, seeking comfort he felt that pull towards her and then he was beaten so badly. Then I think about how he tried to help the last lady that owned him and he tired to defend her when her lover was beating her. That cost him his life.
Then he becomes a Dark Hunter and even Artie won't touch him. I wonder why in the first place she offered him a chance to become a Dark Hunter. If he was so bad that she didn't want to touch him then why let him become one of her hunter? I have a lot of theories on this one. Then to lose his village and have everyone believe that he was the one to kill all those people. He even believed that he killed all those people. I don't understand how Ash could let that happen. I understand him wanting to keep some of the secerts from him, but he could have made it so everyone thought someone or something eles had killed everybody. That was just cruel.
Everytime in Zarek's life that he reached out to people, he was cut down and hurt. He lived with the motto was I gonna hurt you before you can hurt me.
That being said. I think that Zarek had a harder life than Zsadist. His whole life up until he was with Astrid he never had anyone care for him. He never knew what it felt for someone to reach out to him and not hurt him. I cried in both books, but with Zarek's book i cried so hard that tissues couldn't handle it and I had to get a wash rag. There was something about his story that just cut through me.
A side note on Ash..the theories I have about him
In one book I have a certain theory and then in the next we get to see more of him and that theory grows and changes into something more. I have gone back and reread the legends in the all of the first 5 books(Julian, Kryain, Talon, Zarek and Wulf). I figured out a big thing out about Ash and that Lynz thought that I had cheated and looked it up. I didn't. I literally got a legal pad and started writing down names and things said about this person and that person and I had a big 
light bulb moment. I finished Vane's book last night and I am going to take a day or two before I start Valerius book so that my Twinnie, Lynz, will have time to catch up. I love all these books. I am so glad that everyone suggested them.
Sorry for the long post. Z & Z are two characters that I feel very passionate about.
) I'm not a big crier but the letter (you know what I mean) made me tear.
