Is my fiancè too close with his best friend?

Idk if I should weirded out by my fiancè's friendship or not. Me and my fiancè are both 28 and have been together for 3 years. Him and his best friend have been friends since basically birth since their dad's were close friends. I have always thought a husband and a wife should be each others closest friend and we are getting married in a few months. I overheard my fiancè talking to his best friend and they were both wasted and he was laughing about how if they stopped being friends he would have to kill him because he knows way too much and his best friend was telling him he knows him better than anyone. My fiancè said that's true and his best friend asked "Even more than Soph." And I'm Soph. To which my fiancè said "Yeah. You know things about me even she doesn't know. She knows the good, the bad and the ugly. You know the good, the bad, and the trauma." My fiancè has never told me he had trauma. Honestly it sounds like he had a very typical childhood. They're both clearly drunk and yes I'm eavesdropping at this point but they start talking about some of this trauma which lead my fiancè to cry and his friend put his arms around him.

My issue isn't that there's something wrong with guy friends being close. But is it appropriate for him to be closer to someone than his own future wife? I know people will say nobody owes you there trauma but if hes gonna tell his best friend and not me isn't that bizarre. Shouldn't your wife be the person who knows you the most, not a friend?