Visual Studio - Manage Multiple Files That Are Part Of One Class - Classes, Modules?

My VB project is large enough that it requires several files. It was originally developed as a Console App and I created each file as a MODULE. All modules could use subroutines, data structures and constants from other MODULES and everything worked fine. I needed to add basic windowing to the app and this required that the app be converted from a Console App to a Windows Forms App. The main window is Form1 which is not a MODULE but a CLASS. The problem is that some MODULE based functions cannot access subroutines, data and constants that are defined within the CLASS Form1 unless they are incorporated into the CLASS file and this makes the CLASS file very large. If I add a new Class file to the project, it also cannot interoperate with Class Form1 in the same way that multi-MODULE code interoperates.

How does one spread CLASS code across several files and still allow it to interoperate as if it were in a single file? Alternatively, how does one create several CLASS files that operate the way multiple MODULE files operate.I am sure that there are all kinds of best practices that I am violating but the goal to to get some prototype software working and interfaced to some lab equipment.