tl;dr:
yanderes are best. fuck everyone who said something bad about them in past, present or future. Have a nice day!
The long version:
I am blasted away by you guy's ignorance and borderline stupidity for hating on yandere (not exactly this girl but others too) and then "suddenly" "discovering" that her existence is worthless, she was miserable for all of her lifetime, and now being sorry for her.
Don't you guys know that "EVIL" "DANGEROUS" people who love and worry about their loved ones more than anybody else in the world (partly because their life without this little peace of happiness is perpetual hell) is not EVIL™ and DANGEROUS™ people but cornered pitiful souls that cling to their last chance to not live in suffering.
I have seen numerous cowards those are suggesting to push such people away or run away from them because it is more challenging to keep that kind of relationship than to keep your typical tsundere bitch's sadomaso insincere intercourse going or, the best of the voiced opinions, is to sit before your monitor and rot, cause it is troublesome to get involved with someone or somebody.
Also I want to stress out this "MYSTERIOUS" thing for yandere to become very passionate about somebody because of something "insignificant", like joking about marrying smb
or helping them in any way (like helping them on a train station (like in Koharu no Hibi) or finding some important for them). It is insignificant only for you, not for them. Any act of kindness will be like a blinding beam of light if you live in dungeon for all your life. There is nothing strange or not adequate in it sparking their passionate love. It can seem not normal, cause it is not NORMAL™. It is not normal for anybody to suffer 24/7 of depression and/or abuse. Also there is not a straight line of normality that every human being is set on. Everyone has their situation and only it defines their NORM. If you want to become HUMAN#SERIAL#№7132641259 stop reading this garbage with yanderes and "pSyChOlOgIcAl" tag and watch memes from fb all day long. You will become normal very soon with that method.
Anyway, thx for translation and best regards to yandere-chan and her bf!