Moral Business Dilemma?

My partner and I are to open a franchise business soon. We were recently approached by the main competitor to open their first franchise store with a greater return on our investment and less overall risk. We are mortgaged to the hilt with either option, and will spend a long time paying off either business. The business we have been liasing with already has provided a tremendous amount of support and the owner is my partners current boss. We are likely to be better off financially with the second offer, but feel morally obliged to the first party. Any advice?