I think you have to ask him what he meant, see if you are/are not taking it in a way he did not mean (since you say you don't understand what he meant). If you want to be with him, care for him, I would have a conversation with him about it; tell him how you took it and that you felt hurt from it.

To me it sounds like he was hurt, thought you were saying you could not trust him as himself. Taken that way, it is almost exactly like what he said in return (and how you felt). Telling someone that it is impossible for you to ever trust them can really hurt a person (and implies you know the future/don't believe you will ever get better).

Think about it; if I said to you, up front, "I'm never going to trust you." what would be your reaction? Why/how would you continue in a relationship with me? No matter who you are, how you behave, feel, or what you try to do, you cannot come close to me, I will not let you near.