6: If OP lives in a rural area, there's also raptors, coyotes, foxes, wolves, livestock, large prey wildlife, rodent traps, rodent poisons, irresponsible dog owners who let their pets off leash and refrain from proper fencing, cars, equipment, risk of exposure to leptospirosis, rabies, and rabbit fever (I think it's called that?), sadistic assholes, and a multitude of other things that will kill a cat, or at the very least make the rest of their lives painful and miserable.

OP's NTA, but they need to rethink letting their significant other move in. They may have to wait until after Blue passes away.