Help on developing custom Sitefinity Mvc form field.

Hi All,

I am working on developing custom form field and stuck in the middle.
As of now, I have tried the designer and working. However, I was struggling how to display the selected fields in widget.
And, the selected fields should not display in widget while developing the form but it should display on the page.

FYI…

Corticon Association Field functionality can be find at below link. 
drive.google.com/.../view

The files can  find here:
drive.google.com/open

Can you please guide me what is wrong from my side? And, how can proceed further to implement Association field functionality as above video?
Any help would be helpful and appreciated. 
Thanks,
Balu