I liked it. It feels realistic to me. I mean Kiyo decided to stop running, but sometimes that leads to questionable endings. Like maybe this is the bad end, because Ayumi never disclosed her current relationship with rando-guy, etc. Or maybe this is the start of the happy poly end, where everyone gets what they want. In the end, Kiyo made the decision not to run from her problems and that's an overall good thing
Alternate reading would be Kiyo only said she'll be Ayumi's girlfriend so she can use the shower and then book it again when the rain ends. It's not like they live near each other, and Ayumi's in no position to call her out