Loop with row after each second item

loop_row.php

<?php 
  $post         = new WP_Query($args);
  $counter      = 0;
  $start_el     = '<div class="row">';
  $end_el       = '</div><!-- .row -->';
  $item_per_row = 3;

  if ( $post->have_posts() ) : 
    // Opening the first row
    echo $start_el;

    while ($post->have_posts()) : $post->the_post();
      echo ( ( $counter % $item_per_row === 0 ) && $counter !== 0 ) ? $end_el . $start_el : ''; ?>

      <div class="col-sm-6">
        <h2>Content</h2>
      </div>
      <!--  .col-sm-6 --> 
      
      <?php 
      $counter++;
    endwhile; 
    wp_reset_postdata(); 
    wp_reset_query(); 

    // Closing the row
    echo $end_el; 
  endif;
?>