Nee, Boku ga Inai to Shinu tte Itte yo

Will this love culminate in happiness or despair? Toruka is in a relationship with Iori, an ideal, high-spec boyfriend who is the envy of everyone, and with her days going smoothly, publicly and privately. One year into their relationship, Iori proposes to her, saying, "I want you by my side for the rest of our lives." She feels elated, but then she discovers that someone has been stalking her. She enlists the support of her childhood friend Jin to find the culprit, but...!? 24-hour surveillance, wiretapping, tailing... It's the start of a psycho-romance, in which male-yandere warped love and obsession never stops running wild!

(Source: Bunkasha, translated)