I don't know about deal breaker territory. Yet, with feeling short changed, unhappy with other aspects, including lacking -even if by choice- intimacy, the secret lifestyle could be the straw that breaks the camel's back.
Having a secret life and sending you an email from that account displayed a subconscious desire to be forthcoming, I'd suspect?

Yes, keeping a sense of individuality is important. Not need to keep tabs on one another. If this were a marriage, however, then this wouldn't be necessarily about a right to ones own identity, it's suddenly legally and financially relevant.