When I use vim's quickfix to jump to errors in my build, if the file containing an error isn't already open it opens it in one of my splits, replacing the file I had open.
Is there a way to either reopen last closed file in a split or get quickfix to open files in a new split?
You can use :cn :cp :cl to jump to previous/next/list errors in a build. This way you can :bn and then :bp. Or use markers: ma, 'a.
Try using <C-o> in normal mode. It takes you to the previous position, even if previous position was in other file.
If you have the quickfix window open then pressing <ctrl-W><enter> while the cursor is on the error you want to go to will open the file in a new split window.
what I do in this case is the following: before starting the compilation process I first split the window
:sp
After the compilation process I just go to the original window (the one I created with split) and do CTRL-w+o closing other windows and leaving me in the original position.