Do you have any crash logs (eg: launchd_sim crashes) in ~/Library/Logs/DiagnosticReports? If so, can you provide one of them?
Is there anything interesting in ~/Library/Logs/CoreSimulator/CoreSimulator.log?
The issue is that you have DYLD_INSERT_LIBRARIES=/usr/lib/libimckit.dylib in your environment. What is this for?
The iOS 8 simulator will not work on OS X Mavericks if you try to inject host dylibs into the process via DYLD_INSERT_LIBRARIES. OS X Yosemite has software changes that will work around this problem and just log the issue rather than crashing.
I suggest that you either upgrade to OS X Yosemite or simply unset DYLD_INSERT_LIBRARIES (and/or uninstall the rest of the software that is associated with libimckit.dylib).
To make sure that DYLD_INSERT_LIBRARIES is not set, edit /etc/launchd.conf or $HOME/.launchd.conf (eg: sudo nano -w /etc/launchd.conf). Look for a relevant 'setenv' line, delete it, save, and reboot your system.
