Just to throw this out there, (No actual spoilers for where you are) Ami treated Sensei the way he taught her to. She's already seen him at his worst before, knows he wants to be left alone when he's unwell:
And they have prepared items for scenarios like this:
(She was apparently taught to milk him, and help him shit in a bucket)
On the other hand, Sensei's too much of a narcissist to actually take care of someone. He just treated her the way he'd want to be treated, except badly. Like Ami pointed out, she'd never expect him to be able to take care of her anyway:
(She's been marinating in her own issues while taking care of Sensei for around 8 years, hence her snapping. (Ignoring the trauma that the resets have also likely had on her))
Basically, they have a fucked up/"special" relationship where Ami acts more like an adult than he does, and that's not good for either of them, and almost no one besides kind of Maya and Niki understand Sensei's and Ami's relationship (ignoring the optional sex). Hence why both Ami and Sensei noted that others "don't get it":
