My partner did some things that hurt me - is my hurt reasonable, or just a knee-jerk monogamy-culture-fueled reaction?

I have been dating a woman who is polyamorous for almost a year. She has another partner - a guy she has been with for 10 years. For the first 6 months of our relationship, she kept me a secret from him. I knew about him and I thought that he knew about me and was fine with everything, she never told me I was a secret from him. He lives far so I never saw him really or interacted with him. She only sees this guy once a month if that, whereas we live together. So I assumed they were pretty casual- she never really talked to me about this guy, she kept that side of her life very private, I just knew he existed. 

One day someone told the guy about her relationship with me and there was a lot of turmoil with her and him, she never shared much about it with me though. I felt like a secret, and I felt pretty played. Eventually they made up. I was hurt from being kept a secret, but tried to move past it as best I could. I always asked for communication on her part, and that’s largely why it hurt so much. Recently, I saw her writing about one day aspiring to live with her other partner, she never shared this thought with me, and didn’t intend for me to see this, I came upon it accidentally - but seeing it hurt a lot because for the first time I saw that this relationship meant a lot more to her than I had thought. I feel hurt because of the lack of communication and am wondering if this is rooted in my monogamous conditioning or if it makes sense, even in a polyamorous context for me to be hurt by all of this.

YES, my friend, this falls under the category of “inherently problematic and hurtful things that both a polyamorous person and a monogamous person would be reasonably hurt by.” This person lied to you about things being above-board with her other partner, and she lied to her other partner about whether she was with you. That alone would be a strong signal to reconsider the foundations of this relationship and whether she is a trustworthy person. Now, you find out that she has not been honest with you about her feelings and plans for the future, which do affect you.

You have a right to be angry, and hurt. That’s not just “monogamous conditioning,” that’s a reasonable response to your partner doing something that isn’t okay. And if she tries to twist it to make your feelings unreasonable or unworthy of being addressed because somehow doing polyamory correctly means being ok with this, she is gaslighting you and using “polyamory” as a manipulation tactic. There are times where it’s appropriate to say “okay, these feelings are coming from internalized biases and assumptions, and while I can’t turn them off, I don’t necessarily need to assuage them, act on them, or demand changes in response to them.” Trust me when I say this is not one of those times.