I still think it’s heinous to knowingly take part in something like that. Being an accessory to cheating - fully aware of what’s happening - is still cruel. I’d never want to be friends with someone who was willing to do that. That said, the cheating boyfriend will *always* be the common denominator. OP, I’m so sorry you got dragged into this. 😭 I suspect folks would rather criticize a woman who knew nothing than hold accountable a man who deliberately chose to cheat.
No one says you can’t have a fwb, but if you find out your fwb is in a committed relationship, I personally think you should stop sleeping with that person out of respect for the relationship, and out of your own safety. If they’re sleeping with you in a relationship, they’re more than likely sleeping with them too, and STDs are real