I just got my mind blown on Twitter.
Someone wondered, what if Jane Foster broke up with Thor because she knew she had cancer and didn’t want Thor to suffer.
And now I add my 2 cents. What if the cancer is indeed because of her being possessed by the Aether...
One small problem with this is that we know Thor and Jane were still together during the events of AoU (2015), so her cancer must have developed very slowly for Thor to not notice it and for Jane to wait several years until she considered it serious enough to warrant breaking up with him.
Jane living with cancer for 10 years (from 2013 to 2023) would definitely be plausible, though, especially if she got dusted.
As a side note, I found it weird how Thor didn't mention Jane's fate in the Snap during his tearful speech about her and the Aether in EG. I suspect that Jane got dusted and that this only further compounded his sense of misery and failure.