I sense a little too much doubt towards Murakami.
Look at it from her perspective. Moritani was only doing things with her in secret with this strange power and couldn't even keep a simple promise to let her know when she wanted to use it. It probably seemed from her perspective like Moritani saw her as a side fling since she couldn't talk to people.
We all know that's not the case by all the monologue we get from Moritani, but she also thought Murakami saw her as a side fling due to her lack of ability to communicate.
Honestly a super-embarrassing mutual moment in public out of the time-stop was what they both needed to know the other was serious. The mangaka just decided for it to be a pantsu-flash.