My wife and I are both the same age as you (44). Ever since we got married which was 23 years ago we’ve had completely joint finances. We trust each other and are both frugal by nature so it works. We have no rules per se but out of courtesy we’d generally give the other person a heads up on any bigger discretionary expenses regardless of type. Any major expense like a vacation, home remodel or vehicle would be discussed in advance. In terms of roles we used to both work but since we had our oldest who is 13 now she’s been a stay at home mom and I’ve been the income source.