Originally Posted by AnnabelMore
I think that when you're talking about setting an after-the-fact boundary, especially one that may affect your partner emotionally or affect his or her other relationship(s), it's especially important for part of the equation to be you figuring out why you feel the way you do about it and if it's something you can work on.
I feel like this is great advice. Granted, I am completely new to this site, this lifestyle, and pretty much anything else associated with poly but it sounds smart. It's not fair to set an ultimatum to the ones you love by saying 'I don't like this so you can't do it or I'll leave.' It is fair to say 'I didn't like when this happened, it made me feel (insert emotion here). Can we please talk about how we can avoid this in the future?' The problem may be the action, it may be your reaction, or it may be a combination of both.
In my opinion, you would ideally want to set boundaries BEFORE the discomfort/jealousy/anger happens. You just don't want to put yourself or anyone else involved in a position where they are uncomfortable. However, it is hard to anticipate what all can happen and how you're going to react to situations that you've never specifically talked about. Just make sure you make it a discussion and not a mandate, and I'm sure you will be fine!