I am in dire need of help with my relationship situation. Please nudge me in the right direction and be gentle, I am hurting beyond what I ever thought was capable. This is too long and chaotic and I am sorry.
I will talk about myself (32, non binary), my boyfriend who I will call Sunflower (31, m) and the person he wants to date (unknown age, f). I already postet this in another subreddit but it wasn't really seen by anyone.

Trigger warning for mentions of mental illness and abuse, but it’s all from the past and not currently happening.

Tl;dr: I was always polyamorous and I am experienced, why do I hurt because my former monogamous boyfriend wants to date someone else for the first time and how do I cope?

Backstory:

I lived non-monogamous almost my whole life. In the beginning it was open relationships with mostly making out with people of the same gender and since 7 years I am in exclusively polyamorous relationships. Meaning that everyone involved has the freedom to explore connections in a natural way, including love and sex. I made many mistakes over trying out how to have polyamorous relationships and have hurt people in the past with my headless behaviour and I also got hurt by others trying to navigate somehow without experience. I like to think that nowadays I have figured it out a bit more.

I have also been mentally ill my whole life, I have complex ptsd from my family and men. I was in therapy for the last 3 years and it really helped me become a more stable person who is less triggered and who can cope well usually.

1 and a half years ago I was in a bad place, with an abusive and controlling partner who hated me being polyamorous but wanted to fuck as many women as he could and treating everyone like shit. During that time I met my current boyfriend Sunflower, who had a similar relationship where he was abused by his then ex-girlfriend. Sunflower gave me the strength to leave my abusive partner and we fell for each other hard.

Because of both of our issues with relationships and intimacy growing together was not easy. We had many downs but also a lot of ups and in general our relationship is strong and mostly healthy and we connect in a way that I never allowed myself to do with other people. Looking back, my past relationships always were emotionally distant, as I never allowed myself to become too attached and too in love. I never wanted to be the one out of control or relying on other people. I left them before they could leave me. But Sunflower and the loads of therapy helped me to let go of thought patterns of the past and for the first time in my life I felt at home and safe with someone.

I dated two other people in the beginning of our relationship but it never fulfilled me. I am saturated with one person and myself and the busyness of life. Sunflower always lived monogamously before me, but he accepted me being polyamorous and had always wanted to try out this way of living. And of course he has the same rights as me. I don’t own anyone, I can’t control the behaviour or feelings of others no matter what my mental illness tells me. He is a free man. We had the talk about rules for me and him, which weren’t a lot because I know from experience and reading that complex rules are set up to hurt everyone involved. We agreed to use protection, communicate with each other about new connections and that our apartment should be free of other romantic partners, which is what he wanted and I thought that was a sensible request for a beginner. He did not date anyone in these 1 ½ years of being together with me and always told me he is happy with just the way it is and doesn’t feel the need to date others.

Current situation:

Now for the last weeks life was stressful. I am currently looking for jobs for the first time in three years and it has been frustrating and difficult. Also I am responsible for 95% of the household and he works and brings the money in. He sometimes only works 10 days a month and does rarely support me on his days/weeks off. The constant cleaning and keeping up with everything crashes my energy levels often and causes my chronic back pain to flare up badly.

We had a fight about household duties, the only topic we ever fight about and I felt lonely and neglected romantically for a while. We never have dates, or go out, or do romantic stuff together and after 1 ½ years it is starting to get to me. Then he got seriously ill and had to be in the hospital for some days, which was an hour from where I live. I visited him everyday. He did not want me to visit because he has a tendency to push people away when they want to care for him. I was beyond stressed out for the last two weeks.

Last Thursday he was back home for some days and wanted his friends to come over to play magic the gathering, which we play once a week. It always causes stress and pain because I barely manage to keep up with the household and play day means the whole apartment has to be clean. I don’t want to invite people into a home with cat vomit on the floor and dust everywhere. During cleaning we talked about loving women and I ended with saying that I am happy as just the two of us right now. And that was the moment when he told me that he had met someone and wanted to meet her.

He had met her 1 ½ months ago while playing dnd with friends, mostly online. He never told me anything about her, I didn’t know that she existed. They had talked intensively for 2 weeks at that point and she started flirting with him even though she knew he wasn’t single. The start of him deciding he wants to pursue her fits right into the time when we had a fight and I was not feeling well at all.

He explained to her that we have an open relationship and I am his life and he would like to explore the connection with her, but that I would come first, to which she said that this is new to her but she would be okay with it. And then he told her a great deal about me, my life, my personality. Apparently then they decided that they wanted to meet.

When he told me all this he was smiling with the biggest grin and the sparkliest eyes I have seen him with ever. He also was excited and anxious to tell me and he didn’t even want to tell me who she was at first. He made a big secret of it, I guess because of internalised shame. He waited 1 1/2 weeks after deciding he wanted to see her to tell me about it and on top of it he told a good friend all of this one week before me.

For me the whole thing feels like “Hey, I have connected with a woman and I will meet her and she wanted me before she knew I was in an open relationship and also this all happened while you were feeling the lowest of low and also busting your ass to take care of everything including me in the hospital while I was pushing you away on purpose and also texting her all day and by the way I told her everything about you but I will not even tell you her name haha, I never done this before, what a funny day.”

I don’t think his intent was malicious. I think that he is just his clueless, carefree self and had trouble communicating because he never experienced this before. Well, he experienced my way to communicate two times and he was happy with how I did it back then.

Right now I feel hurt as I have rarely felt before and I don’t know why. I have years of experience, I have had relationships where I had metas and it all worked somehow, I know the theory, I know that I don’t own him nor do I want that, but I am still scared shitless of the thought of him fucking around and finding out, as in tripping over the typical beginner mistakes with open relationships and hurting everyone in the process. Which in my opinion he already did because of not telling me and keeping it a secret. Also it feels weird that she was going for him when she only know that he has a relationship and that he doesn’t seem to mind. I am also scared because of him having lived monogamously before, will he leave me when he finds someone better? I cannot cope with the thought of him thinking about someone else in a romantic way and I hate myself for it. I didn’t care in past relationships. Why do I care now? Why do I hurt? Why do I want him all to myself? I don’t want to feel like this. I want to be the cool, experienced partner who congratulates him, who gives him tipps navigating if he wants to, who is laid back and chill. But I am not chill. I am angry at myself for having all these feelings, of not being able to live what I lived before.

I am crying since thursday and he told me that after my extremely negative reaction he will not pursue her anymore. I told him to wait with decisions until I can think more clearly because I don't want my mood to effect his freedom and I feel like it is unacceptable for me to veto out of hurt.

But I also feel like the life that I had and the dreams and hopes connected to it have vanished. There is nothing left. The plan was to marry and to have children in the next few years and I know that you can have that living polyamorously, but if he would ask me to marry him right now I would say no. I would say he needs to have more relationships outside of me, so I can see that it works long time before I tie myself to a person that way. Because right now I see all the failures that I myself experienced, but also the things I read about on reddit and elsewhere, where it didn’t work out. And I want it to work out. I love him in a way that I never experienced before.

I feel like the last three years of therapy were nothing, because this minor thing triggers me right back into my deepest fears. I need advice on how to cope with my feelings, because I really really really want him to be happy and I would rather be unhappy than selfish.