Insert ad or image after first paragraph

I’m using the below code to insert ads/images after 1 paragraph. It functions properly, however, the ‘Next Page’ functionality stops working.

Is it somehow possible to add ‘wp_link_pages’ somewhere within?

Any guidance would be appreciated, thank you.

<?php
$show_after_p = 1;
$content = apply_filters('the_content', $post->post_content);
if(substr_count($content, '<p>') > $show_after_p)
{
	$contents = explode("</p>", $content);
	$p_count = 1;
	foreach($contents as $content)
	{
		echo $content;

		if($p_count == $show_after_p)
		{
		?>
AD CODE
		<?
		}
		echo "</p>";
		$p_count++;
	}
}
?>