Soo I'm in a situation and trying to figure it all out. I want to do things correctly and ethically.

My partner and I have been together for a year and know each other needing a year and half, we have been through many things in this relationship but I've been patient and given grace throughout it all, I'm not perfect and have had my moments in the beginning of this relationship ship but I've been doing all the reading and learning and have a therapist. I work on a uniqe situation ever is very close quarters and that's where I met my partner. I had a boundry which is normal for this dynmaic when it comes to co workers and future coworkers as I work in a group of 6 people so issues can destroy that group which I've experienced many times i explained everything and he understood and agreed. This is his third contract and he met someone but said they where just friends he was excited about having a platonic friend who was also a personal of color and who also had adhd ect. I was so happy they had that. Before I came to visit they let me know they liked this person but said it was just that and they enjoyed the friendship. But also this perfusion had a partner and more are thinking of opening their relationship. And she may want to chat about how it's been for me and ask the things that go along with it. I visited and the visit was very hard. I felt disrespected many times by this other person and could clearly tell at least from my side that they like my partner and I was like a catalyst and things where being done on purpose when ever I was around. There a whole lot that goes into this but hope you can get an idea. This whole time i told my partner how i felt and what's been going on, be didn't see it, do i just shut it all down and kept going on dealing with it trying to be nice and include this person ask the whole being constantly stared at by all his friends like everyone knew and i was the bud of a joke.I leave the visit to go home. The next day my partner tells me they had a talk and she confessed she did like him. Then the next talk she says her and her partner want to have a 3way with him. I tried not to think much into because he knew my boundry and always said he wouldn't perspective this because it's their first time they have not done any work or research, I was always hoping he would acknowledge that this was a boundry for me, we had a talk and I could see he wanted to do this but I felt so much guilt and shame for my boundry so i removed it he said thank you. I asked if it does happen as I didn't want to control but just let me know in advance when you where having another talk or planned for more with them so I could find a friend to be around or not have it sprung up on me and could just be in a better environment after many other hard times. The also was ignored and I got a text just before it happened which was another blow. I felt many emotions. It's been a rough week. And he asked what I needed. I talked to my poly therapist and she said I cant control or say you can't do something. I agree. But I could let him know how I feel and why and what I need and why and that boundry and let him choose. I know for him it did not feel like a choice since one he loses me and the other he loses that other person in that aspect. But I just feel so horrible like never before. I feel wrong. Aits.