Show related content based on shared reference entity

create a block view that filters for content-type-1.
add a relationship for "Entity Reference: Referenced Entity" for the entityreference field on content-type-1.
add a second relationship for "Entity Reference: Referencing entity" (note the difference from the 1st relationship) and select the 1st relationship in the drop down for this one (it won't appear if you haven't already created at least 1 relationship).
this is the 'money' step: Add a contextual filter for "Content: Nid", select the 2nd relationship then "provide default value" and "Content ID from URL".
and finally, to exclude the viewed node from the list you need to add another "Content: Nid" contextual filter, don't select any relationship, then "provide default value" and "Content ID from URL", and scroll down to the 'More' fieldset and select the 'exclude' option.
This will give you a block view (place it on all nodes of type 'content-type-1' at admin/structure/block) of all the content-type-1 nodes that reference the same entity as the one selected in the entityreference field of the node being viewed.