The image on the left is a ToolBox of VB.NET, not a ToolBox of Excel VBA. As you can see there is a built-in splitter control. Unfortunately VBA does not have a splitter ActiveX control like VB.NET. Can't this control be used in VBA? The answer would be yes.
But we can substitute another control for a splitter control. Here is a sample how to make an image control using like a splitter control using Mouse events.
1. Place two TextBox controls (TextBox1 and TextBox2) on the Userform.
2. Place an Image control (Image1) between above mentioned TextBox controls.
0 - fmMousePointerDefault to 9 - fmMousePointerSizeWE.
same color of the background color of the Userform.