Verified answer

He means that you know him long enough to know bad things about him, but that's wierd for a friend to say this, bc it sounds like he wants you to tell him bad things about your bf like he's bad in bed or has a small penis. I wouldn't trust that friend of his if in fact he is a real friend. Just bc your bf is reserved, why does it mean you can't trust him. If he's shy, he's less likely to hit on another girl for one thing. If he lies to you, you shouldn't trust him. If he's shy, that has nothing to do with trust. If he's outgoing with friends and shy around you, it means he doesn't trust you.

It means you've known him long enough to know a bit about him, not necessarily bad but secretive. Don't worry about it, I got a lot of crap from my boyfriend's friends early on, just a scare tactic

There's a lot more about him that he knows, that you bf not telling you. Or may have said or done something while dating you.

just means uve known him for a while so uk alot about him ex: secrets, insiders, personal stuff etc.