Mad at God over what? Because He hasn't forced your husband against his will to give you what you want? Your husband is the one that changed. So why are you taking out on God what falls on your husbands shoulders?
And perhaps there is something to be learned from what you're going through, and God doesn't change it because the growth you will experience will be more valuable than just zapping you and making you better.
I make bad choices. I do, i wish i made better choices, but i don't. And sometimes i pray and beg for being protected from my choices and wonder why God doesn't intervene sooner, or even help me after more. But one thing i've learned is, each bad thing i've gone through, i've walked away with something from it. Just recently i had my own heart broken, but despite the hurt, i learned about myself, i grew as a person and am better off now, in many ways, than i was before the hurt. I'm still healing from the hurt, but i'm also grateful for the lessons and growth. I walked away with something good out of a bad thing. Maybe this is what God has in store for you. Refining you in the fire.
Not that God Wants you to go through this. I've no doubt He would rather your marriage reconcile, but if it cannot, then He has to make the best of things for you. And sometimes that means we don't do things the easy way.
I've not been married and i don't full know what you're going through, but i know how you feel. I've felt those same types of feelings many times throughout my life. Its difficult to see any good now or in the future when you're in the midst of the storm. But that's what faith is. Trusting that there is an end to the darkness and something better that you can't see. Sometimes we just have to hold on to that hope because that's all we have left.