What are the rules for blocking someone after a breakup?

I was getting ready for a night out when I spotted a "hey girlie" text from an unknown number flash across my screen.

"I'm Danny's girlfriend and I saw some messages from you on his phone. I was wondering if you could help me?"

My eyes widened as I read the word "girlfriend." I've never opened a message faster.

SEE ALSO: Why social media algorithms hurt after a breakup

Danny (not his real name) and I had been embroiled...