I recently purchased Sonar X3 for my pc but I switched to mac after several pc crashes. Do I have to purchase the software again in order to install in on my mac. I thought Sonar was only a windows based DAW but I recently read online that they have provided software availability for both platforms.

Sonar is PC only. There is no Mac version.

People who really want to run it on a Mac install a program like Bootcamp or Parallels on which they can run Windows

Content removed as duplicated earlier answer posted while I was typing.

You can install multiple copies of Sonar on different PCs as long as the registered owner runs only one at a time.

PC crashes means your PC needs a knowledgeable tech to fix it, and/or configure it.
 
I support dozens of MS based computers. Nearly all "crashes/hangs" are related to user changes and installation of programs without reading the install dialogs.
 
Have had numerous problems with users installing Adobe and Java updates and NOT unchecking the install virus scanner options.  3 virus programs running does not make a happy computer.
 
The Mac will succumb to the same lack of attention, eventually.