I once walked in on my best friend sleeping with my ex-boyfriend. We had been broken up for 7 months and it still hurt like hell, because he was my first love. That's why you don't sleep with your bros ex boy-/girlfriend. It's been 12 years since then and if today one of my friends would sleep with him, I wouldn't care.
So the inherent theme of the bro code is: Don't hurt the feelings of your friends. You might have put your mutual friends in a bit of an akward situation, but you didn't break the "bro code".