<?php if (have_rows('columns_carousel_slide')) {
$count = 0; ?>

<div class="item active"><div class="row">

<?php
$multiplier = 1; //that could actually go before the while
if (count(get_field('columns_carousel_slide'))%2 === 1 &&
    $count === count(get_field('columns_carousel_slide'))-1) {
        $multiplier = 2;

print_r(get_field('columns_carousel_slide'));exit;

} ?>

<?php while(have_rows('columns_carousel_slide')) {
the_row();
if ($count > 0 && (($count % 2) == 0)) {
?>

</div> <!--.item -->
</div> <!--.row -->

<div class="item">
<div class="row">

<?php } ?>

  <div class="col-md-<?php echo (6*$multiplier);?>">

        <h2><?php the_sub_field('columns_carousel_slide_title'); ?></h2>

  </div> <!--.col-md-6 -->

<?php $count++; } ?>

</div> <!--.item -->
</div> <!--.row -->

<?php } ?>