my photos library wont open (most serious apple issue i've had so far)

The restart probably fixed it. Rebooting clears out a number of temp caches and swap files and often fixes "glitches" like you experienced. Occasionally a boot into Safe Mode by booting with the Shift key held down will further help clear out files and repair directory.  Then reboot normally.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Just be sure to have a backup strategy enabled so if things do go south you have a backup you can fall back on.

You can use your Photos library only from one user account. Photos has been designed as a single user application.

If you want to use the same Photos Library from several different user accounts, the library needs to be on a separate volume or partition, where you can set the "Ignore ownership on this volume" flag. And you cannot use fast user switching. All users that have used the Photos Library need to be logged off, if you want to use the library from a different user account, because your library will be in use, as long as you are signed in.

Prepare the separate partition or volume as described here: Move your Photos library to save space on your Mac - Apple Support