In the end, it seems to me, you have to do what you think is best for you. The big box retailer would cut you loose without a second thought if it suited them. If you get the new job, try to give your current employer an appropriate amount of notice & leave on a positive note. That's really all anyone can expect, in my opinion.

I recall, years ago, I had worked for a big box retailer for just a short time when another much better opportunity popped up unexpectedly. I felt kind-of sheepish bailing out after such a short run there. But then it wasn't perhaps more than a year later, they closed the store. Isn't that just the way it goes...