Well it isnt TOTALLY ridiculous. Perhaps OG will agree that he will try a monogamous relationship with your bf
That is between them. Of course I usually assume anybody who is like - hey lets be mono FWB while we aren't really friends and I have actual relationships... to be somebody who is going to be told "oh sure" and then whining a month later all surprised that a person who agreed to that went off and had their own relationships because they didn't consider your request to be real since it's so ridiculous. Hopefully if OG is thinking "no thanks I like your gf too" he manages to express that (otherwise is he really ready to be in a healthy
poly relationship at all?)
YOU however, yep, sounds like you'll have more negotiating to do. I'm guessing you've written posts before but I don't recall them directly. I hope you can do a firm "these are my boundaries, and this is what I wont accept" sort of statement to your boyfriend. And yes, even a - well no, if you have sexual partners I am going to also so lets discuss the reality. check never hurts.