The truth is the hardest thing to tell, but after it's been told, I brings you a peace of mind and a clear conscience.
I will edge you to put aside your fear of the guy rejecting you and open up to him now before he gets to find out later from outside. Hearing the truth from you personally will some lower the hurt than him hearing it outside (that will break his trust in you forever).
Don't just tell him the truth. But also make him understand that you're a changed person now. As for the father, present your case to God and He will punish him where it will hurt him the most.
That's my mind oo.