Am I wrong for being mad?

My husbands sister came to visit (from different state) and recently we have went through a big financial change. Between bills, gas money, groceries we basically have nothing.

My husband tells me his sister is poor and he wants to give her $300 dollars to go back home. I told him I didn’t think this was a good idea, that it’s simply too much for us to give right now and maybe give less instead…I get it’s his sister but in my mind, it would put his own family in a bind. He states “I know what I’m doing, don’t worry we will be good.”

So he sends it and what do ya know? Next day he says unexpected bills came and we are very low on money. I told him I needed to order groceries still and he proceeds to tell me to make it cheap and don’t go over a certain amount of money. I get irritated and tell him this is why the money he gave his sister was a bad idea. We could use that right now for groceries, gas, diapers, wipes, etc. he gets angry and tells me his sister is his sister and he will do what he wants. So now we are literally struggling and I’m just upset but idk if it’s wrong to be .