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Was that the extent of the plot? It (sort of) describes the end of Saishuu Heiki Kanojo, but that series has a lot more to it as well.
Nope, that's not it. I think that WAS the plot: it's After the End, the dude is dying, and he and the android gal are basically spending both of their final days being in love and making love.
Might be Ai-Ren that you’re looking for
If I recall correctly, this manga takes place in a post-apocalyptic setting, with a dude and an android gal basically boinking and growing closer romantically before the dude kicks the bucket. Anyone know what it is?