3 months I know but I drew that comparison just now and gods, it's actually quite closer than I initially thought. When a person just hurts by existing / being around they just won't go because just because they "love" someone despite knowing that the other person is hurting to at least some degree which is beyond their control.
i'm so glad you realised it!
I got worried because a lot of people in the comments seemed to feel pity for the amoeba and saying they need "a ending where him and the protagonist could stay together" and things along with those lines.
...That's exactly how the bait of a toxic people/relationship works....