By design, the IDE should not be displaying the files side by side at the same time. Related files (such as .cpp, .h, and .dfm for a given Unit) are displayed as a group, where there is only 1 tab up top for the group, and separate tabs down below for the individual files of the group.
If you are able to display the individual files side by side with their own top-level tabs, then the files are likely not being grouped together correctly, such as if the file names do not match each other, or the header file guard in the .h file is named incorrectly.