If I start dating someone and they never mention that they're poly, I just assume they aren't and keep the relationship monogamous. I don't really like it when it's opened up, either. It's hard to tell if someone agrees just because they like me or if they actually want to open it up.
That being said, if someone cheats on me in a monogamous relationship, I'm mostly pissed because I would have said it was fine if I had known that's what they wanted. That being said, it goes both ways so they would also have to understand that me being okay with them being with other people means I can be too. My first poly relationship was with an ex who only opened the relationship up for herself and got pissed off if I even jokingly kissed my friends.
I think the hard part is if you're the type to crave nicotine when you're extremely stressed out. I go through cycles where I'll quit nicotine for a year or so, and then something really difficult would happen in my life and I'll start back up again.