There are a number of people who everyone should be able to rely on and best friends fall into that number, but what do you do if your best friend decides to hook up with your ex? This is possibly the worst form of cheating that any partner can do to their girlfriend/boyfriend because not only did they cheat, but they were cheating with the so-called best friend and that's a special kind of pain. How do you handle that? How do you feel? There can be multiple thoughts going through your head, like, "When did they start?" "How long has this been going on?" "Who's to blame?"
Do you turn and blame the ex for eyeing your best friend behind your back or do you blame your best friend for being sneaky?
Do you write off your ex as the worst human being in the history of ever or do you forgive your best friend when they say it only happened once? Who do you blame, if you can blame anyone at all?
It's quite simple. Blame them both. Your friend wanted your ex while you were with them and your ex wanted your friend - all you have to do is figure out who wanted who first. Don't pin the blame on one over the other because they're both guilty and should be ashamed of themselves. While they gained each other, they lost you.