(i am going to address the trust issue, because everyone else has pretty much covered the money issue)
To be honest, I am hearing some immaturity on boths sides here. And it is obvious that neither of you totally trust. He didn't trust that he could be honest with you, for whatever reason. You don't trust him because he lied to you. This is a vicious cycle that is imperative to fix NOW, early in the marriage.
My best advice for you is, do not start your marriage parenting each other. You both need to trust each other, that takes some time and openness without judgement. The only way that will happen is if you both feel that the other person is approachable, not judgemental and rigid. It is really just as important 'how' you talk to each other as what you actually say.
If you have made it clear that there is a possiblity of you thinking he is a 'weak' person in your eyes, he will definitely not want to be forthcoming when he blows it. And you
both will blow it, in one way or the other, over the years.
About a year and half ago, I messed up big time. I never lied and never cheated, but I was Playing a game with another girl, being stupid with a guy.
Actually, if you were not totally forthcoming, you were lying to him. Maybe not outwardly, but still deceiving him on some level. Accept that and recognize that you both have it in you to be deceptive. All people do. But neither of you deserve permanent punishment for making mistakes.
I think the reason people end up continually lying to their spouse is because they, as a couple, really never learned to accept one another as imperfect human beings and one or the other learned, early on, that telling the truth only got them punished (scolded) by the other. People avoid being parented in their intimate relationships, at all costs. Lying is the easiest way to avoid it. Doesn't make it right, just reality of the human condition.
The person you are married to is supposed to be the 'soft place to fall'. That stage is not set when there is criticism and judgement. When you blow it and the other person says, "Man, you really hurt me...it really hurts that you felt that you couldn't be honest with me. But I can forgive you, know that I am the one who loves you the most, lets find a way to get past this, let's solve this together. " That is what creates a trusting environment in a relationship.
You both will have to prove to the other that you ARE the soft place to fall by being compassionate and open minded. By being forgiving rather than punitive. That is part of the trust process.
Why do we love and trust our parents and friends? Because they accept us, ugliness and all. That same atmosphere is essential in marriage.
If the problem really isn't the maxed credit card, but the dishonesty, approach the situation as a big mistake. Show him that he hurt you but can come to you, that he can be honest to you. That you are the soft place to fall, his partner...not his judge and jury. I guarantee if you do not parent him, he will be more honest with you.
I am not suggesting just rolling over and accepting dishonesty in your relationship. I am saying work on the trust issue together. Don't set up scorecards, learn to be partners. You are starting out, there are bound to be bumps in the road.
It takes more than saying "You have to be honest with me", it takes
showing each other that it pays off to be honest. That is a journey, not an event.
Good luck to you both!
The thing that I'm wondering about is if there are other maxed-out cards/debt that you don't know about. Perhaps now is the time to pull both of your credit reports. I do this every year anyways, to make sure that they are correct and to check for identity theft. 
