They finally finished looking at all of each others tattoos.
The sex wasn't what it was cracked up to be.
Kat reached her level of commitment
They didn’t have a free spot to get a tattoo of each others name..
Two more for your list:
They decided to let their egos get married instead.
Hillbillies like James and Von D would rather keep it “common law” and not make it official with them thar law-type folks at the courthouse.
Neither one is capable of coloring between the lines... OK, maybe Kat can...
Seriously, this is one of those celebrity lashups that couldn’t possibly go anywhere. You cringe when you hear of it.