I kind of think this didn’t need to be a deal breaker. This wasn’t an intentional lie to cover up something he did to hurt you. It could be something he didn’t tell you because it’s not an easy thing to deal with. Personally I think it was probably a painful ordeal for him and he might have felt ashamed. People are very judgmental toward others in a situation like this so it’s very likely he closed off this part of his life to everybody, even himself. I agree that it would have been better to tell you up front but I think it’s worth having an open conversation with him about at least - after the initial shock wears off. You would know right away if your first opinions about this were right or if there is another side you hadn’t considered.