The key to getting better about this stuff is to communicate with your partner and discuss needs and ability to spend and to come to difficult and annoying decisions together the way you do with the fun and awesome decisions. If I was in your shoes, price wouldn't have been asked either because that purchase is not appropriate when we have so little money in the first place. So you're a bit of an asshole to yourself for "saying yes" to this when you knew you couldn't afford it. Sure, you had the money, but that doesn't mean you could afford it. But you are far from the asshole in this situation, I just think you're undermining yourself.

He's definitely the asshole here, not because of the game and hiding the cost, I actually think he likely didn't know better. (And if he did and manipulated you, ignore my point because he's totally the asshole) But I think he's the asshole because he didn't know better and isn't trying. He is relying on you to get better about money and tell him what he can and can't do rather than take initiative to learn himself. Remember how I said the key is communication? He's not. He's wanting you to mommy him. And you're letting him get away with it, and now he probably thinks you're the bad guy here cause "he asked".

This is an ugly hole to be dug into, but it's well past time for a proper talk with him about financial responsibility in the relationship, goals and individual as well as joint spending habits.