Bad Dreams

I've been tormented lately by horrible dreams of a dreadful person I once loved. If I'd been acting reasonably at the time I would have seen that this person was dangerous; I can quite easily imagine a future for him that includes prison time. In my dreams, I will get into a taxicab and suddenly out of nowhere he'll jump in next to me; I shove him forcefully out of the cab and tell the driver to step on it. Or he's always at my shoulder and I can't shake him. There is so much that I wish I could forget, so much humiliation and grief in remembering who I have been and what I have done. A priest who had a conversion told me once that it's Christ who separates our old life from our new, but that it's salutary to remember from where we came. Is it? Is it also then salutary to harbor regrets, and to know that only God can set right what we have made wrong? And can we trust Him to do that, even if it happens at some later time and we are forever unaware of it? How do we go on with a knowledge of our past, which highlights how undeserving we are of the gifts of the present?