Ok, she just don't give a damn about their dating relationship. She decided to go out with Rei because she didn't had any reason to refuse.
She treats Rei like any other of her friends. When she's sad she comfort her, angry she tease her, happy she lets her be. And in between she tease Rei with her dating expectations. I don't think she is doing it with pure malice. It's just the way she treats her friends, maybe.
But the only thing that I don't like about Ami is, she's taking Rei as granted. Like no matters what she does she will always come back because she loves her.
Also, using the same cliffhanger as the last chapter... Come on author.