OP, you have to face the fact he won’t change, so you need to change YOUR mind set otherwise you’ll tie yourself in knots.
Accept it will always be this way, and if you want something, you’ll have to sort it. Like you’re doing at the moment with YOUR finances.
If he complains, simply tell him he has a choice. If he says you made him change his car, tell him ‘he has a choice’ if he moans about money, tell him ‘he has a choice’ that choice is to continue with his job, and have the lifestyle he’s got now, or get another job. Don’t tell him to do it, that’s on him. If he continues to whinge just ignore him, but stand firm. No more ‘helping him out’, make sure he does his fair share. Being tired, or needing to work is no longer a negotiation, he’s a father and partner, his child, you and the household chores are none negotiable.
My dh could earn 6 figures and has done, he now earns 30k a year. Which is fine, but he has to accept that with this decision comes consequences, such as no flash car or holiday. I used to get het up about it, but I now don’t bother. If I want a flash car, I work hard for it. If I want a nice holiday with the dc, I work for it. I just try and take the emotion out if how I react to him. I can’t ‘make’ him do anything. That’s his choice