I hope what I am going to say makes sense, but basically, he gets so obsessed with Penelope that he will do whatever it takes to "safe" Penelope from her house. He believes she is unhappy there (he is not wrong, though) and that her family is mistreating her. For that, he finds Yvonne and brings her home, thinking that this way Penelope will be able to escape the ducal house, now that the true daughter has come home. Problem is that Penelope didn't want to meet Yvonne just yet (she appears sooner than in the original game), and frustrates all Penelope's plan. Feeling betrayed by Eklis, she just tells him that she doesn't need him anymore, and well, there's a loooot more going on, but I hope this helps a bit. I also have to say that Eklis, apart from being obsessed with Penelope, he is partially brainwashed by Yvonne, which makes him even more dangerous