The statement above was said by Rose in Lion 3:Straight to Video. She also said I'm going to become half of you.
This makes sense until you remember that "existing" to a gem isn't the same as it is to us. A gem is still alive as long as it's gem is intact. A gem's body is a projection that isn't real. The actual gem/gem(s) are the only real and permanent part of a gem. Rose is still existing so what did she actually mean?
Let's look at it as if she was a fusion.
Rose Quartz can not exist with Steven because half of her fusion is now half of Steven. Like Opal can't exist with Sardonyx or Sugilite. So she unfuses and is no longer a fusion named Rose Quartz because she literally can't exist at the same time as Steven.
Make sense?
VOUS LISEZ
Steven Universe Theories (Continued)
RandomThis goes along with my previous theories! I hit the limit on the other book.