Macro to store previously selected cell

I am creating an excel app that has to check to see if the previously active cell is empty or not.

I am having zero luck storing the address of the active cell and keeping it after changing cells.

Purpose of Application Example:

If B2 is active then store address of B2 and add combobox to A2.
If active cell changed to B4, check if B2 value, if empty delete combobox in A2 and update stored value of previous cell to new active cell, else update stored value of Active cell to new active cell.

Any help with this would be greatly appreciated.

Thank you in advance.