hello! if i'm polyamorous, should i get into a relationship with someone who is monogamous?
I wouldn't advise it - read through the archives of my blog to see a lot of examples of this not working out. But then again, the only people who write in to an advice column are people who need help with something. There could be tons of people out there in perfectly happy mono/poly relationships.
It's okay for some things to be dealbreakers - what are yours? Think through what you're willing to give up for that relationship. Don't go in hoping that you can change their mind or work up to opening up the relationship. It's okay to decide that you want to try and make it work. It's okay to decide that it's just not meant to be. Ultimately, that's your call.