I'm trying to create an order item list for items that are being purchased and my relationship to the item table does not pick up the appropriate items properly.

Another table lists the items that could be purchased by customer and it appears that in the items being purchased it is selecting only the first item referenced for this customer.

I've attached the relationship chart for reference.

Son_relationship.pdf

What is the purpose of the CustomerPurchase table?

Your lineitems table should reflect the pricing for a particular invoice. If you want to use a particular custom pricing schedule, the foreign key for that pricing schedule should be in the invoice for the pricing lookup.

Also if you want the item description for your line items, you should have another Table Occurrence to your items table from the OrderLineItems TO.