It's actually, gameplay wise, to be strictly avoided to "win" the game.
The point people play the game is for weight gain. Which is easily achieved by feeding the girl and getting her fat. The fat ending literally is what a lot of the people here came for, easily get it.
Just because there is an ending where she doesn't become massively fat, yes, the ending where you avoid to "win" she still gets fat, then what's the problem?
The game is still worth being played. It advertises itself as weight gain and it provides it.
You are literally crying over nothing.