Looking for advice SharePoint groups and Sharing

I currently manage who can see a list item by changing the Sharing. This works fine most of the time.

I want to be able to create a custom form for a SharePoint group, but I need to change the sharing so that only people in that group can see the item in the list.

I have tried to Share the item with the group but that hasn't seemed to effect the visibility of the item in the list.

Any suggestions?

@smithme,
Something like this may work?

Dear @smithme,
By "visibility of the item", do you mean its visibility in the List View?