Can I Sue? I REALLY NEED HELP!?

Hey everyone. I helped open a sub shop starting april of 2009 for a friend of mine and drove over 50 miles a day commuting. Well, We moved the sub shop up nearer to us, and i set up the sub shop and did all of the work to set it up. In December of 2009, Me and the owners fiance/girlfriend came to a business agreement that I could not come to agree on, so I left after the fiance said some hateful words, and I left. Well, I was the lifeline of that business, and knew 90% of the things they didnt, so I went on an interview at a bank, and did not get the job because of the past reference. Let me clarify this one thing; I was not paid one paycheck and did all of the paperwork and basically started the business, while i was promised that I was partner, I come to find out that that was false. My friend (an attorney) said if they slandered your name because you left and left them clueless, that is Defamation of Character, and I can sue. Is that True? Im not the type to sue (never did, never will) but they are trashing my name. Im going to find out what accusation were said, and will have to get those doents. Please Help!