[eluser]cahva[/eluser]
I downloaded the zip, checked those files but lost interest as I got better things to do than review your whole code and not knowing what is the real problem you're having
Could you just pinpoint the problem you're having?
For the simplest, adding related products is quite simple. You create a table for it for example products_related with 2 fields, product_id and related_id and create a relation between the products using those. Then use that data as you wish. For example create a method get_related($id) to your products model which will return all related products to that id you pass to it.
