maybe we should take a step back and ask if you agree that a married couple should have their own personal bank accounts and maybe a joint savings account and another joint account where they pay the bills out of.
I don't see any issue with that, but I do see an issue with both individuals having their own account, them sharing a joint account, and then one of those individuals having an extra secret account which they are skimming off some of their income or savings or whatever to hide from the other person. In such a case you obviously do not trust your spouse, which goes back to the initial question of why did you marry them in the first place?
I have argued long and hard in defense of all things privacy, and so if you want to keep parts of your life secret from your spouse than that is absolutely your right. I guess I just don't understand why you would be in such a relationship. If I trusted someone so little, I would be keeping a much more casual relationship with them.