It sounds like he may have reacted to some recent life stressors (argument, marriage, shopping addiction recover) by having a relapse and making a large and impulsive purchase to relieve that stress. As with any addiction (recovering alcoholic here), he's now compounded the stress. He's now further in debt and carrying the guilt and shame of that, plus he knows he's keeping it a secret from you because he fucked up.

Call him on his shit. Tell him you know and ask him what's up. It's the only way to make a relationship with an addict work. My husband knows that he has two options: he can support me, or he can enable me. Support means having tough conversations. It means not taking excuses as answers. It means being willing to walk if it comes down to it.

It sounds like he needs to see a therapist, to learn how to cope with stress without resorting to addictive behaviors. Cognitive behavioral therapy is one of the most effective treatments for addiction. Insist he look into it, because if his behavior remains unchecked, it will only get worse. And now you're legally along for the ride.