Don’t assume all relationship that is polyamorous nonmonogamous, but the majority for the people i understand are. Why? The concept of nonmonogamy isn’t going to be too outlandish because if you’re game for polyamory, which is fairly outside most cultural norms. Having said that, you can find monogamous polyamorous relationships — threesomes, foursomes, and moresomes who’re committed, intimately and otherwise, to one another.
Set boundaries whenever you’re starting, but understand that these boundaries might alter as your relationship develops, plus it’s OK if they do.