This might seem a bit out there, but creating an accountability system or checks and balances in your marriage is the first step to dealing with finances as a married couple.
We all need to be held accountable. While self-discipline sorta comes in waves, some of the time self-discipline can waiver. I know for me that is at least the case.
Maybe I am hyper critical of myself, but just buying a new truck was only making one person happy = ME. We are naturally selfish creatures. Having a significant other is all about being selfless.
This might sound weird, but there are people out there who do not know how to pay bills on time. They don’t know when their money hits their account and when it goes back out.