Pay bills or buy stuff? What is more important?

My husband is known in his family and mine as being very irresponsible with money. He is a truck driver and recently took a higher paying job. My mom paid cash for our house and we pay her the mortgage. He has not been able to pay her in 2 months and is getting paid soon. He is insisting that it is MORE important for him to buy an inverter to run his fridge and microwave in his truck than to pay my mom. She has been thus far lenient with paying- but she is becoming more annoyed w/him and has threatened to throw him out (she would not throw the kids and I out, only him she says). He just threw a tantrum (he is a 30 yr old man) and said that unless I let him pay $150 for that inverter, he will start buying the highest priced meals he can at truck stops because "he isnt living off a dollar menu". His parents have told him to PAY HIS BILLS, which includes a car note that is a few days late. He refuses, saying that thing is more important and will save $. What is right here? We have 3 kids.

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