Unbrother

"Unbrother" is a informal term used to describe someone who disregards the bond of brotherly love or friendship, even though they are not necessarily blood-related. It implies that this person has disregarded or betrayed the trust and closeness associated with a brotherly relationship.

Xuan Li: I am unable to go to the club with you guys tonight.
Kevin: Its okay, i'm used to it, you're an unbrother