In regards to friendship, the cardinal rule is never dating your friend's ex-boyfriend. When a close friend and their hunny break up, being a friend means you dont try to date, mack, get with, or hook up with the ex. Breaking this rule defiles friendship and ruins bonds and all friendly love with the rule breaker in the circle of friends.
After Max broke up with Sid, Alexis, a 'friend' of Sid, broke the cardinal rule and started dating Max less than a week after the break up. Sid and Alexis' friendship was ruined and Sid soon learned that no one gave two squirts of piss about her emotions, regardless or what was said.