AnimeMangaLover4Ever

My friend is heading towards the Yandere genre (which, btw, I'm a little bit scared as I'm enabling it, but he's harmless.... I think), and he wanted some recommendations.

I'm trying to remember this manga where the girl is the yandere, and the boy is the MC. It starts with them in elementary, where the yandere kills off the boy's friend/interest. It then time skips to when he's in high school, and the yandere tortures the one girl friend/interest he made after he pushes everyone away, especially girls as he's scared she might kill them ( which she did but tortures them instead).
She then goes away, and they haven't seen each other for like 10 years? Throughout the years, he's been tormented by the memory of her and wants to kill her. But, when he finally gets the resolve to do it ( thanks to his high school interest sister (she wants revenge on her sister for being tortured and being depressed)), he visits her but finds out she lost her memory.
If anyone remembers, please let me know. It's been on my mind, and I feel like this is a good enough manga to scare him away from the genre

To all the people who have worked hard in getting mangago back, Thank youIt had been a torturous month without you. But, guys remember to go and write down your manga list, just in case something like this happens, which I hope doesn't