Determine your claim to rage

There is no one-size-fits-all appropriate response to when you find your closest compadre has been shacking up with your ex. But, let's be real. Was she your ex, or was she a girl you occasionally poked? The gravity of the relationship plays a large part in how much anger you're reasonably entitled to.

Things to consider when formulating a response:

• How long ago did you break up? Have years passed since you called things off, or was homeboy hitting it the minute she hit the market?
• Did you break up with her? Were you over it (or fronting like you were) to the degree that your friend would have likely assumed he'd be good to go? Or, was it a known fact among your boys that she left you whimpering for weeks after the split? 
• How did he approach you about the situation? Did you hear it through some convoluted game of telephone, or did he break the news himself? 

There is a difference between being blatantly malicious, and genuinely believing it might not be an issue on his end. Recognizing the difference between the two determines how appropriate your response is on the scale of ambivalent to legitimately livid.