First, remember that Apple has redefined what was originally called “Finder”. It no longer does what it’s name implies.
Second, you can still ‘force’ Finder to display your own Library directory in the Finder Sidebar, like anything else you’d want to put there. Use the Finder->Go menu (one last time!) to select “Library” or just type shift-command-L. You should now see the contents of your (user) Library (“~/Library”). You can select and Drag that label into the Finder Sidebar. It will remain there until you change it or Apple decides what is better for us.
NOTE: Be sure to check/enable “Show all file am extensions” in Finder Pref->Advanced tab.
To see the “temp”, “var”, etc directories, just select the standard Apple hard drive volume in the Finder Sidebar. I think in Finder it is a “Locations” section of that Sidebar.
Finally, I highly recommend Pathfinder and just keep Finder hidden.