Jek attacks Ritsuka in order to retrieve the Forbidden Grimoire, thus, he doesn't feel anything for her and wouldn't hesitate to kill her if this is needed to take the Grimoire. At Azuna's death, he even laughed which showed that he does not care about Ritsuka.
Jek seems to be confused by the fact that Lindo attacks the vampires that attempt to kidnap Ritsuka. He only sees him as a vampire (who is later revealed to be a dhampir) getting in his way. He appears to know that Lindo is Nesta's son.
Nesta is Jek's master, whom he serves faithfully, carrying out Nesta's orders without hesitation.
Jek is the one who killed Azuna.