After he was done drinking Hecate's blood which made him feel refreshed, Zoravec pondered over what he could have given to Devi when he marked her with blood pact. It also made him mildly concerned regarding what her deepest desires might be. He realised that he might have made a mistake by not considering the consequences of his actions. And it was possible that he also might have provided Devi with something he should not have.
After all, it was evident that his blood was powerful and possessed the magic to bless people with different qualities. Zoravec had been too focused on satisfying his own desires, and now he was faced with the uncertainty of what he had given to Devi. Just like he had no clue that feeding on Hecate's blood she would be blessed with youth once again. Zoravec could potentially see the value of his blood and at the same time it also posed a threat to his life.