Why didn't Yuno
kill 2nd Yuno
earlier? As in, before she and Yuki had the conversation about getting married and stargazing (August 1st I believe). Didn't she know that
Yuki would get upset if he found out that the Yuno that he made the promise to was dead?
If she had done this earlier, then there wouldn't have been a need to hide her secret from Yuki, besides to avoid exposing herself to Deus.