Remember that silly ass rule that you aren’t allowed to date one of your friend’s exes or someone they liked? It made sense when the person in this case was someone you considered a real friend aka someone you communicate with daily, share secrets/confide in and spend time with each other’s family. Of course in that case it can be considered betrayal depending on how your friend feels about said ex. Your friend may feel disrespected and never want to speak to you if you do decide to cross that line.
I’ve always been a person that believed it’s an excuse to stop another person’s happiness especially if you don’t consider the person a friend. That has been something I’ve noticed a lot these days. The ‘no dating a friend’s ex’ rule does not apply to someone you only know from social media. Just because you like each other’s pictures or leave a comment here and there doesn’t mean a friendship was built. It’s social media and If we’ve never exchanged numbers and attempted to build a friendship outside of cyberspace your feelings don’t mean much to me.