I don't like this, because I sense the axe-kun. It is really hard to see how the relationship can evolve or change from this point onward. Alien yandere GF basically has MC infested and physically mutated. The only thing left intact seems to MC's mind at this point, but damn I see the 'Horror' tag. Rest of the world can't do shi* to change or stop said Alien-yandere GF's mind nor actions.
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Author or write can try to write something out, but at this point I'm skeptical the writing can get better. The power dynamic between the Alien-Yandere GF and every party involved thus far in the story just doesn't compare and nothing else interests her besides the MC.