Is that Lillian at the end?
Wasn't she going to marry a prince (Eve's ex) and live happily ever after? What the hell is she doing, running after Eve?
Houston, we have a yandere.
There's a manga by Kodama Naoko called Uminekosou Days. Have you read it? Me, I read it in Spanish, long ago. I know a group started translating it to English at some time, but I'm not sure if it was completed.
Anyway, in this manga, at the beginning, the mc Mayumi is dating a guy and they're planning to get married; but Mayumi's bestie Touko seduces him and pushes him to cancel the wedding and break up with Mayumi. Mayumi is very hurt and leaves the city. She goes to a seaside resort where she meets Rin, a young woman who runs a boarding house, and they fall in love. After a couple of months, a frantic Touko arrives to the resort. Turns out that Touko dumped Mayumi's ex-fiancé as soon as Mayumi left the city, and has spent all this time looking for her... and now that she has found that Mayumi has a new lover, she's determined to ruin this relationship as well!
It's never explicitely stated, but it's obvious to the readers that Touko is 1) more than a little unhinged, and 2) obsessed with Mayumi. She feels jealousy when Mayumi gets close to other people and always tries to sabotage her relationships, wishing to forever remain her one and only. All of this is eerily similar to the thing between Eve and Lillian! Eve says that Lillian has always been her only friend... but isn't that because Lillian chased away everyone else? And when Eve got engaged, Lillian stole her man; and now she has left him to come again after Eve! And she's even attacking guards, she must have totally lost her marbles!
This is what I'm getting from the story so far: I get from Lillian the same vibe as Touko.