Originally Posted by Ameyuri
My boyfriend and I decided a few months ago to try out poly relationships
I'm currently moving in/trying to get a new job/having major stress
says to me that you guys timed your decision to try poly poorly. Even in the best of circumstances, having multiple relationships increases the time and attention one has to give and generally increases the stress factor too, especially at the beginning.
So unless the moving in/trying to get a new job/major stress is fairly new and came up AFTER the decision to try poly, I'm left wondering if you're (consciously or not) okay when you're the one with multiple partners but less okay when the shoe is on the other foot. You say you were "sort of" okay with it until the transgression, and that this is hard for you. Is it possible you're jealous less of him/his time and more the fact that he's dating someone and you're not, particularly if the agreement to try poly was fueled by you wanting to date women also?
Wanting to meet someone he's seeing is reasonable, especially if this is someone he wants to spend a week with (which DOES seem a little excessive). But you being his "main" relationship isn't the strongest justification, unless that's something the two of you agreed to as part of your experiment. A significant number of poly people don't have "main" and "other" relationships. They just have multiple relationships. Now, if you two live together, share bills, chores, etc., that adds a layer of, "You're staying somewhere else and barely even informing me? Seriously??" but we don't know how entangled you two are so it's tough to make that determination.
Hopefully you two can improve your communication and expressing your wants and expectations, since it sounds like it's the dissimilar expectations that are the biggest hurdle at the moment. I agree with Annabel that a big-time slow down may be in order, at least until communication between the two of you has improved and some of the external stresses are dealt with.