Here is a tutorial on how to revert your steam to the old friends list and chat UI.
If the steps below don't explain this well enough, someone else made a video tutorial for this as well:
Step 1: Navigate your way through the steam directory until you are in the steam folder, like so in the image below.
Step 2: Create a shortcut to your steam application by right clicking on it and clicking "create shortcut".
Step 3: Right click on the new shortcut and then click "properties".
Step 4: Go to "Target" and write
"-nochatui" "-nofriendsui" as seen in the image below.
Step 5: Drag and drop the shortcut into your desktop so that you can easily launch it without having to navigate through the files to reach it.