Post source link plugin – small modification

I’m using a little plugin that allows me to add source link to every article. I found the code in this thread: Article source link for posts

It’s almost perfect, but I need to make 2 little modifications:

  1. When there’s no source link, the word “Source:” is still showing up (here’s how it looks like: https://i.imgur.com/orY1Msf.png), but I need to get rid of it if no source link is added. Does anyone have any idea how to do it?

  2. Source link shows on every page of a post. I have some posts splitted into multiple pages, but the link still shows on each one of them. I need to change this – the link has to show up only on the last page of a splitted post. Any ideas how to achieve that?

Here’s the code I’m using (pasted in functions.php): Article source link for posts – the first one

And here’s what I have in my single.php (single post):

<div class="source-link">Source: <?php echo esc_url( get_post_meta( $  post->ID, '_source_link', true ) ); ?></div> 

Thanks in advance. Im desperate for help.

Kacper