The install script tries to make that all automatic for all systems, but clearly that’s not working for your system.
It sounds like /Users/Morgan/bin/particle wasn’t added to your PATH. Perhaps try running particle ... from that directory to make sure it’s installed, and then add that to your PATH.
It might be nice to see the logs from the install script to see what went wrong.
If you have dfu-util installed, and brew and node and npm already, you should also be able to install the CLI globally with:
npm install -g particle-cli