After a dysfunctional childhood how can I learn to trust the man to whom I am engaged?
We are able to learn to trust people when we are in relationships where those around us say what they feel intuitively, and then act in accordance with what they are saying. With people who are mature their intuitions, speech and actions all coincide. This is what love is.
Because you grew up in a dysfunctional family you may struggle to have you intuitions, words and actions concur. You may then be projecting this dysfunction onto others and find it difficult to trust them. So as well as learning to release your pain, the other task I want you to practice is to learn to have your intuitions, words and thoughts concur. Practice being a completely trustworthy person yourself and you will find it easier to trust others.
What I have suggested is a suitable first step, however you may wish to source some support in your journey back to trust by finding a good local psychotherapist or art therapist to help you in your journey into your pain or perhaps you could both go to a local marriage guidance counselor (it is important that your partner understands how you feel).
Further Help and Resources
Ayal Hurst has some good words to say on the subject of trust, particularly in trusting your own intuition, because these things begin at home, within oneself.