Let me give you a bit more context.
We had a shared account to cover our shared life. He was a selfish git with expensive tastes, and he spent 'our' money on things we didn't need (and that I didn't want). When he became an alcoholic, it was worse because he wasn't just buying junk, he was buying wine and literally pissing our money away, but I'm not sure it was that much more expensive. He'd already been wasting a lot of our money, but rather than spend it on stuff, he spent it on drink (part of the reason why I didn't immediately spot how much his drinking had ramped up).
Not everyone has an alcoholic partner; I'll give you that. But a selfish partner with a very different attitude to money? That's more common.
I think it's also common for couples to compromise and buy things they wouldn't otherwise buy. If store brand is good enough for you, but your partner prefers a more expensive version, do you buy store brand, or do you go for the fancy one? These little things add up.
As a single person, I'm in control of my own budget. And in that respect, things can be cheaper.
Thanks for your kind comment, btw - I didn't miss it. It took me a long time to realise that I'm not just financially better off but emotionally better off. I vowed to myself never to get in a relationship again that didn't somehow make my life better. Well, none of the options that have presented themselves have had the potential to make me any happier than I currently am. So, unlike the OP, I am content with being single. I enjoy this lifestyle of putting myself first.
I would never have been able to afford a property with my ex.