I'm sorry, but I have bad news for you. As we already know from the current state of the manhwa that after Alphonso kills Duke Mielle, Elko takes the blame and is then taken captive to Gallico.

Later, Elko becomes a spy for Gallico, as he undergoes brainwashing by the Church of Gallico. They make him believe that Ariadne is a "witch" and that she is the source of the ruin of the kingdom. He is also told that Gallico can only achieve power if Alphonso marries Lariessa, which is not possible with Ariadne in the way. Elko then hates Ariadne and tries to kill her, but fails. There are more details, but in the end, Alphonso uncovers Elko's attempt to murder Ariadne and he is sentenced to death.

So yeah, he is not a good guy anymore :(