Gentleman ≠ Bro.

Being a 'Gentleman' is one thing. Being a 'Bro', is another.

But both are equally as important.

If your bro broke up with her girlfriend, it's mildly OK to hook up with his ex. Ex chick is NO chick. She's free. But;

#1 : Seeing that she's single, you approach his ex to hook up. That's being a gentleman.

#2 : Seeing that's she's your bro's ex, you ask for his 'permission' if it's OK to hook up with her. That's being a true bro.

Both are a very different situation, but mind you that both are as equally as important. Chivalry is not dead, and brotherhood lives forever.