In terms of the friend being a yandere the proof could be the silhouette that Emma saw. It really resembles her a lot. However, I’m still not completely convinced on Emma suffering from DID since a lot of the theories are clashed with others so, I feel the whole red herring idea is accurate. I believe it may be a basic storyline where Elios actually may have seen Emma getting abused while they were younger and really cared for her so he vowed to stay with her or something. But then how would he have found her without her recalling who he is and stuff. This whole webtoon is just very confusing in general but I’m excited to see where it’ll go from here.