
Here you go....
1) So basically Eclise goes full on yandere for Penelope and becomes extremely possessive and manipulative.
2) At one point he asks Penelope to run away with him but she refuses and tells him that it won't end well so he should get that idea off his mind.
3) So he decides to betray her by bringing Yvonne back to the Dukedom so that Penelope would be abandoned by her family now that the lost daughter of the Ekcard family is back. So after she is abandoned and left alone, she would have absolutely no one to rely on except Eclise and thus, he could have her all to himself.
4) Penelope becomes absolutely devastated by his betrayal and she makes it clear to him that he can never have her like this.
5) Later when the Crown Prince falls for Penelope, Eclise decides to kill him and take over the whole empire cuz he can't even stand it when Penelope talks to another man, let alone just sit back and watch her marry the Crown Prince and give birth to his child.
6) Eclise then tries to kidnap her but she escapes and says that even if he succeeds in taking over the empire, she will never love him. But Eclise is like he doesn't need her love, just having her and keeping her by his side is more than enough for him. He then kidna ps her for the second time and locks her up in a room but the Crown Prince later shows up to save her.
7) So at the end, Eclise dies while protecting Penelope . But he reappears in the side stories so it turns out that he is actually alive.
Damn I liked Eclise the most so went to read a lil bit of spoiler and then asdfghjkl WHYYYYYYYYYYYY?! (╯°Д °)╯╧╧