During covid and lockdowns DP and I both ended up in jobs working fully from home, we decided to utilise this and go down to one car between us, sold DP's and began sharing the costs of one car (petrol, tax and insurance). We both owned our cars outright but DP didn't get a lot for his so I just told him to keep it in his savings rather than putting it in the joint account.
Circumstances earlier this year changed as we changed jobs within a month of each other and both needed to spend some time in the office (DP 3 days and me 1 day), we struggled with sharing the car between us for a month or so before deciding actually it would make much more sense going back to 2 cars. We had recently come into a substantial amount of inheritance from his family (which went straight to our joint savings) so decided to use this money to purchase a decent secondhand car but agreed that as we could afford it would pay that money back into savings each month 50/50 over 3 years to replace what we had used, we had a very detailed conversation at this point that we would treat both cars as ours, split all costs for both cars 50/50 and we could just use the cars interchangeably based on our work requirements.
After purchasing the car DP realised he could only have one number plate on the car parking at work and as our office days were the same one day of the week he would always have to take the newer car. I was a bit annoyed at this as my office is much further away (2 hour commute) and the older car isn't as reliable or fuel efficient but it was what it was and I just put up with it.
DP is changing jobs again and will now need to spend 5 days a week in the office. I mentioned this morning how nice it would be to take the newer car (as its just a nicer car all round) on my day in the office now he's starting his new job. He laughed and told me no chance.
So AIBU to stop treating the cars as "ours" when clearly DP sees the newer car as his? Why should I be paying for a car which I only get to drive on a weekend when that is the car we would use anyway when we go out as a family as its bigger. I may as well use the money to upgrade my own older car for something more fuel efficient and nicer to drive for my commute.