You have the :hover pseudo on your CSS. While this exists, the behaviour persists.
You can add a .small-window class to your <html> tag and control it with that.
https://jsfiddle.net/9a1n8xtw/4/
$(window).on('resize', function() {
isSmallWindow = $(this).width() < 768;
if(isSmallWindow) {
$('html').addClass('small-window');
}else {
$('html').removeClass('small-window');
}
});
And the css
html:not(.small-window) .headline:hover + .content {
display: block;
}