One takes a breath, but one breathes. One loathes something, but one is loath to act in a certain way.
No one in the world has ever been loathe to do something, except maybe in the seventeenth century. It is never an excuse for your idiocy that orthography was only standardized two hundred and some years ago. That was before you were in school, and you can zip it.
And the pronunciation helps you out. In both cases the "th" sound shifts. Of course this does not guarantee a change in spelling, but it implies one. One has an "e," and one does not. In a vacuum, you'd have a fifty-fifty chance, but if you've ever read a book, you should know.
They are different words. They are different parts of speech. Pin the tail on the donkey is not a useful approach to spelling.