This is also my working theory, but I am leaning towards Summer being in a vegetable state / brain dead.There was an old game I suddenly remembered while thinking about this game with some similar points about healing from trauma.
Have you guys ever heard of or played the old Japanese visual novel, Kimi ga Nozomu Eien? It released back in 2001 and I do believe the title was localized as Rumbling Hearts or something. It was popular enough to have an anime adaption back then, which for that time wasn't as common as it is these days for JP VNs.
Without going too much into spoilers or too deep into it, it was basically about the protagonist in a relationship with a girl who gets into an accident and goes into a coma. He blames himself because, if I remember correctly, she got hit by a car or something while on a date with him.
She remains in that state for so very long that and the protagonist is left struggling to get through life and with depression, barely eats and his place is a complete mess. However, there is another girl who is his friend and does her very best to help him heal and get through it, takes care of him with everything she can, including feeding him often and cleaning up his place for him and being there for him emotionally.
Eventually, she helps him recover and get back to a normal life and he starts a relationship with her. And everything was going smoothly and well, until the girl in the coma suddenly regains consciousness and the protagonist is torn between the two girls:
The girl who helped him recover and heal, and did so much for him and spent so much of her own time devoting herself to help him, or the girl who wakes up confused in an older body many, many years later who he feels responsible for.
It also resonates (with me at least) with what he says when the car accident Victoria has, he says something like "I am wondering if it would better you to die here instead of enduring it all", I would not think that you would say something like that if you did not go through it yourself or someone dear to you.
And I don't think that the accident he was in was bad enough.
What we also know is that in the cabin was the last time they touched, but he saw her one more time.
Everyone keeps refering to her as "lost" not dead, it also seems that they say that with great care.
We also know that Nami is partially responsible for his trauma.
We also know that Nami caused them to be picked up at the cabin by the police officer.
I think that this car accident happened on the way back from the cabin, him getting collapsed lungs and Summer in such a state that lead her to be brain dead, which is the last that the MC saw of Summer.
After that the summer's parents took Summer home, and they did not like the MC so he is not allowed to visit.
You have a good point here, I agree that Ocean would not use that plot point twice.I don’t think Summer is in a coma, i imagine if she would be, Bella‘s sister wouldn’t be in a coma too or Ocean at least wouldn’t have shown it to us.
Now even more leaning towards vegatable state