Being upfront with him is the first step. If you truly love this man and want him to be a part of your life, you have to trust him. It's unfair to him to have to build trust where someone else broke it, but it's a fact. If he is willing to accept this that's great. He obviously knows about your past. Let him decide if he wants your baggage. He might willingly offer to help you carry it.
When we love someone, we do insane things to make them happy. It might seem like he's being unnaturally easy with you regarding this but perhaps he just loves you and wants to make this work. We look past many flaws in those we love because we see something even better behind those dysfunctions and we don't mind scaling a few walls to get to it