Left? Never left, just added on.... Servers FreeBSD, OpenBSD used to install from one floppy with FTP/DSL. Desktop is mostly OS X but I also have Ubuntu (drag and drop straight from the file manager onto a server halfway around the world with ssh/sftp. The cloud made easy.) Legacy equipment support amazing 12year old scanner runs as new.
No need to leave. The freedom cannot be matched.
Learning order that I would recommend Linux > Windows > OS X > FreeBSD one after the other and keep them ALL.
Linux before windows because some thing windows does it seems like magic to a new user due to the fact that it is hidden deep under many layers once you understand these basics they are the same on all platforms. OS X when used with standards is amazing. When you lock your stuff up in a garden I feel it's hard to move you off. Get rid of iTunes, iCloud, iPhoto or any iXXXX it's a selfish way to enjoy your files and it limits how you share your stuff. It gets in the way.
I Love computers, just saying...