In a relationship of 3 years the Father to our son just won't let go of my past. He thinks "the past will repeat it self" me cheating on an Ex is haunting our relationship. It doesn't help that I was his first EVERYTHING either. Need help I make sure the sex is good house clean bills paid.

You can't generalize about all men.
We can't know why your man won't let go. I'm sure part of it is the fact that you were his first. Maybe he even finds it convenient that you act so guilty and try so hard to compensate. But at some point you have to say to him 'I'm not going to grovel for the rest of my life. The past is the past. You are not those men. I was younger then and more foolish and impressionable. There are no more ways I can prove that I love you and our child. Please, do not bring up the subject again. It does no good.' Then go on about your day with a little coolness, hurt, and reserve - but not petty or mean or angry.