how to know last click of load more button php ajax - php

Question

I have successfully execute a load more button functionality using
jQuery - AJAX load() Method, it works like this , display first 3 comments from my db when the page is load , if user click load more button it will load 3 more comments , user click once load 3 more comments until there is no more comments from db.
The problem is when there is no more comments from db , user has to scroll all the way up. which is not very user-friendly, I know can make back to top link to guide user go back , are there any alternative solutions ?
like detect the last click or when there is no more data from db comments , then show less (display only first 3 comments), just like facebook style.
here is my codes
<script>
$(document).ready(function(){
<?php if ( more_than_3_reviews($the_post_id) ): ?>
var reviews_count = 3 ;
$("#show_more_reviews").click(function(){
reviews_count = reviews_count + 3;
$("#show_more").load("ajax/load_comments.php", {
new_comments_count : comments_count,
post_id: <?php echo $the_pro_id; ?>
});
});
<?php else: ?>
$("#show_more").remove();
<?php endif; ?>
});
</script>
my backend php file
if ($_SERVER["REQUEST_METHOD"] == "POST") {
if(isset($_POST['new_comments_count']) and isset($_POST['post_id']) ){
$comments_count = $_POST['new_comments_count'];
$the_pro_id = $_POST['post_id'];
$approved = "approved";
$stmt10 = mysqli_prepare($connection,"SELECT comment_name, product_id,comment_msg, date_time FROM comments WHERE product_id = ? and comment_status = ? LIMIT $comments_count");
mysqli_stmt_bind_param($stmt10, "is", $the_pro_id , $approved );
mysqli_stmt_execute($stmt10);
mysqli_stmt_bind_result($stmt10, $comment_name,$product_id,$comment_msg,$date_time);
mysqli_stmt_store_result($stmt10);
while(mysqli_stmt_fetch($stmt10)){
$get_comment = <<<DELIMETER
<div class="media">
<a class="pull-left" href="#">
<img class="media-object" src="http://placehold.it/64x64" alt="">
</a>
<div class="media-body">
<h4 class="media-heading"> {$comment_name} <small>{$date_time}</small> </h4>
{$comment_msg}
</div>
</div>
DELIMETER;
echo $get_comment;
}
} // post get comments
} // if its POST request
any assistance would be appreciated .