About five years ago, I worked for a small company and got to know the top executive very well. His wife had died three years earlier and it was clear he was lonely. There was a 27-year difference in our ages, but we began dating, which led to sex, and vacations he paid for. He was very helpful in getting me on my feet financially and professionally. While I knew the relationship would end, I also knew he was getting emotionally involved, but I could not break it off because my job was great and I was finally making enough money to pay off bills and have a normal life after many years of not having much.
He left the company and we kept seeing each other, and when the time was right I asked him to help me get another job in a larger company, where he knew the executive staff. Using his influence, I got a great job, and after several more months I decided it was time for me to move on and begin my life over with people my own age. He completely broke down on me, something I did not expect, but I stuck by my decision.
This larger company had a layoff and I lost my job. I applied for another, and the interviews were going great until one interviewer noticed the small company where my old friend and I worked, and asked if it was okay to call him for a reference. The next day I got a call telling me there was no further interest in me as a candidate. I called my old friend to ask what he had said, and he acted as if he did not know me and cut the conversation short. I need him on my side for this job search. How do I get that after I dumped him so badly, and how do I apologize for this?
I Messed Up
How about, "I made a huge mistake, I dumped you before my career was secure, and now I need to remedy that by reeling you back in just long enough for you to get me another job."
The problem here isn't that you "dumped him so badly." It's that you dated him so badly. You consciously led a lonely, probably still grieving man to believe you cared about him, just to pay your bills and advance your career.
I don't think there's an apology to cover that one. And even if there were, it could pass for sincere only if you felt compelled to make it in order to make him whole. Would you be revisiting this breakup at all if you still had your job? Don't even fake it.
Some people reading this will write you off. I hope you don't do the same. But you have only one ally left. Truth. Admit to yourself that you used someone emotionally for material gain; admit it to him, but only if you think he'd derive some satisfaction from it (absolution, you'll be seeking elsewhere); and, finally, admit to interviewers that he can't be a reference because you had an unfortunate personal relationship with him.
Plan B: Entering a new career field. Vertically, I suggest.