Also you can be in a polyamorous relationship and still cheat. It all depends on what structure people are consenting to, where everyone’s boundaries are. Granted it is more rare but it still happens sometimes. For example I have a pretty strict boundary where I don’t want any of my existing partners to start dating any of my new partners until I’ve had a chance to establish the relationship dynamic between me and the new person. I would consider any of my partners crossing this boundary to be a type of cheating.