Pretty great writing, even visually translated with the self-imposed distance on the sister. Tanuki realized how selfish his endeavor can be, but at the same time, he is right to be wary.
Any other person, getting a part-time would be no big deal. But the sister seem to still consider herself a burden, and now that she thinks she sees him getting along with Mochikuzi, she's taking this as a cue to push herself out.
Funnily enough, that's even the opposite of the psycho girl wants, so the sister is not only ignoring what she truly wants but what everyone else wants.
Truly, you can't love someone that don't love themselves. She's not a burden but literally the revolving part of this beautiful mess. Do not leave the bosom of those wholesome yanderes! She's even safer than a president with those two around