Rin should teach a masterclass on teasing your SO. Damn, that's cute.
I really hope she's just doing this to tease him, though. Mental unhealthiness isn't a joke... that aside, DID/MPD developing might be the only "reasonable" explanation why she might show a yandere side too. I'm just not sure how that will play out? Probably her just becoming aggressively overprotective of him?