Yeah I agree there could have been heaps of conditions used all over the place to determine the MC's personality (sex with all the HOTs, being turned down by M&J or being the one that turns them down, cumming on Heather in the hot tub and so on). And definitely, a lot of those experiences would have had an effect on him.
But being in a throuple, that shit is next level, even if the game doesn't actually give you much time to realize how awesome (and potentially complicated) such a relationship would be. At the same time, you're in a relationship with Maya, a girl that Quinn has been taunting and fucking with since the game began. That would influence the MC's attitude towards Quinn too.
You could argue every single variable's use, or lack of use in each branch, but I think people just don't want to accept some things 'cause it doesn't turn out they way they like.
Just change the code, my game is totally butchered, mainly for laughs though.