Tell or not

I have met a tremendously nice man who says he's in love with me now. I am 53, he is 58. He says anything I have done in the past is forgiveable and no one at our age hasn't made mistakes. He's very religious but does seem to feel judgement of humans lays with God, not man. 23 years ago I had a relationship with my brother in law at the time he and my sister were divorcing. I had a daughter out of this relationship. She is my only child. I'm no longer with this man and my sister has forgiven me. However, I still feel extremely guilty! I want to tell my boyfriend but I am afraid he will judge me and will hold it against me and therefore; the relationship will be over. I don't know how I can't tell him when my only child is a result of that relationship. What should I do?