Odd - after my divorce that's what my sister said - "Opposites attract but they can't live with each other". And in hindsight she was right. My ex had put a trip to California on a credit card and I attributed that to youthful foolishness since she was 23 at the time. That was something I would never have done. However, at age 25 I bought an airplane. The distinction was, I think, that I knew I would later be able to sell the airplane and get back most or all of what I had spent to buy it. You can't "untake" a vacation and sell it.
The ex left when we were already flat broke and I refused to even consider taking out a loan for a trip. I was more concerned with "silly stuff" like the curling shingles on the roof, the "iffy" septic system, fire-prone aluminum wiring in the basement, the aluminum windows that rattled and leaked air, house payments, insurance payments... you know, all that boring responsible stuff.
DW has a SIL whose spending reminds me of my ex. Where these people get the sense of entitlement I'll never know.
And DW is often even more frugal than me when it comes to spending. For example, next month we're going to DE to see my sisters. DW initially wanted a hotel with an ocean view but blanched when she saw the prices, so we got a room 20 miles inland for a third of the price, and both are the same distance from my sister's. It's a big gathering and all the spare rooms at their houses are already spoken for.
