I agree with the other posters–it’s business, so do what you need to do, be professional about it, and move on. No biggie. My brother was offered (and accepted) an engineering position with Boeing a few years back, but then was offered another job that was a better situation for his family. He backed out of the Boeing job, and it wasn’t a problem. Think of yourself like a fist in a bucket of water–when you remove the fist, the water fills the spot as if the fist was never there. None of us are irreplaceable. Best of luck to you.