My understanding of infinite scrolling is that you show a certain number of something. Then when the person viewing your page scrolls down near the last on then you use AJAX to get more results and insert them into the page.
Since what you’re showing are not posts, but related posts from a post object field I think that you’re going to be mostly on your own.
I’d start here: http://codex.wordpress.org/AJAX_in_Plugins
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