alright Garth you're just going for it huh, well you'll need to considering that Yvonne is at this point literally going "I am the sole singular person Elsa cannot be with". Like she's not even going we can't date because we're both women, it's specifically "I'm the villainess and thus the only person on this planet who couldn't be the one for her".
But Garth doesn't know about the Villainess System. Nobody knows, not even Elsa.
If other people knew that some kind of god-like power forces Evie to periodically hurt Elsa, and sometimes hurt her REAL BAD, they would understand better Evie's contradictory feelings.
As it stands, nobody has a clue... and Elsa is just puzzled by Evie's wild mood swings from passionate attachment and possessiveness to trying to push Elsa as far from her as possible. (◞‸◟;)