My story is probably a bit different from the rest that are here. I identify as a lesbian so (almost) all of my relationships have been with other women, which is certainly a different dynamic than heterosexual couples.
I met my first wife in high school. We were friends for two years before we started dating three weeks before graduating. We finished adolescence together and began adulthood together, and honestly neither of us were prepared for it. We went to colleges that were 6 hours apart at first, and by the end only 4 hours apart. It was still difficult. Neither of us were really financially independent for the time we were in college. I ended up getting an associate's degree and getting a full-time job while she was finishing up her school, so I got a bit of a head start on the finances.
While I was fairly open about the money I made and enjoyed buying her things, she didn’t really have much involvement in my finances at that time. But when she graduated university, we got an apartment and moved in together. At this point we decided to merge our finances and I added her to my bank account, and she received a debit card that accessed the same funds that I primarily earned.
I don’t think the sharing of finances was really a point of contention, although it did become annoying when she would spend $200 on whatever the moment, I got my paycheck. It was more the lack of funds that really caused problems. Despite me working full time for the entirety of our time together, she struggled to find work that she enjoyed doing and thus bounced between jobs a lot. Finances were not what ended that relationship, but it did cause problems.
I am not married again yet, but I am engaged to my current partner who I have been with for over three years now. We have not merged our finances yet and I am hesitant to do so this time. While we use one another's funds fairly freely, what is in our accounts is very much still our own rather than just one shared pool of resources. We share often but we don’t give each other unconditional full-time access. I think it works better because I no longer have to wonder where my money went and have awkward conversations. Now it is a conversation we have beforehand, and we do have an open-door policy on asking each other for money and we pay bills from whoever can afford it at the time. I think it works better and keeps us from unneeded conflict.