Just disconnect the CD/DVD from the Virtual Machine when not in use by the Virtual Machine.
Have a look at: VMware Fusion (menu bar) > Help > VMware Fusion Help > Managing Virtual Machines > Configuring the CD/DVD Drive > Connecting and Disconnecting the CD/DVD Drive Without Using the Settings Window
Hint: Click the CD/DVD device button in the status bar and select Disconnect CD/DVD and then when needed select Connect CD/DVD.