This shit always gets me. He was her everything, and he just tossed her away because he couldn't keep it in his pants. Just like in school days, it hurts to see someone in pain like that...
'Tis sad to see, I can only imagine how Yuno is feeling. Being abandoned by someone she loved dearly and known forever; by someone who cheated on her to have sex, but never had sex with her even though she was his girlfriend. 😔
This ending wraps up that Negoto can't be changed. Think of it being the same ending as Future Diary.
Yuno loves Yukki to death, but would still kill him so she could be with her. Insert infinite loop.
It's just one of those sad endings where people die.