In our situation its got nothing to do with trust why we don't have joint accounts. We were together for 4 years before we got married..what worked for us with bills, worked for us..so we didn't change it. We've now been together for almost 13 years and keeping it separate still works. I do better with money when it's on a debit card..he prefers cash. I know exactly what's being spent b/c I'm the only one swiping on the account. We honestly never really argue or fight..but when we do money is never one of those things.
I hope that I didn't offend. I actually had a much longer post but erased it for fear I would step on toes. I know it works for some people, I just couldn't do it.
For me joint finances is one of the cornerstones of very successful 25 year marriage.
We tried separating accounts once years ago and it had two major flaws for us.
1. She had access to my account and vice-verse so when she was light one month and wanted some thing I just gave her the cash and she did the same for me when the situation was reversed. I wasn't going to make her go without something she wanted when I had extra so the overhead of two accounts became more trouble than it was worth.
2. There was always a tension around money and how to divide it up. % of household earnings? 50/50? and then who gets what bills? Does the person paying the natural gas bill get extra in the winter and the person with the electric get more in the summer? How do you deal with an emergency when one person has been very frugal and can pay for repairs to the car that were unbudgeted? Do they get punished for not spending? Crap like that kept popping up and it was causing more disagreements than it was solving so we ditched it.