>>3 Glad it's both beautiful and helpful.
Anyways, I don't really frequent anime as much and I'm not that aware of Yandere characters. All I can think of is Future Diary aka Mirai Nikki. Even so, I haven't yet finished the anime. Google them and I'm sure some will pop out.
I hope you will figure it out because like you said, it will affect the future of the story, but I know you can do it. Good luck.