I don't necessarily know how to navigate my feelings and it's driving me crazy

TLDR: Newly polyamorous and had a very positive experience so far, however not entirely sure how to deal with the negative emotions in a healthy way.

I will start this out by saying that I am not asking anyone to babysit me. I have read every article, every reddit post, watched every video that I could and I still have a bunch of feelings I could just simply not sort to their right places. I also have a great therapist who I can talk to, but I desperately need someone who actually experienced polyamory to see their outlook.

Warning: long, messy, and sometimes a bit incoherent post ahead.

I have been living in a monogamous relationship the past two years firmly thinking I am monogamous. To make things even more complicated, this is my first serious relationship and my partner has an ex who they have a child together with. This will be semi-important in the story.

I am not particularly healthy mentally and I am struggling with lots of things that come naturally for other people, and i am highly suspecting that when me and my partner got together, I was having a hypomanic episode.

Despite all of this we had a fairly okay-ish relationship, I truly love him and most of the times it still seems like he also loves me. However, the lows in the relationship were very low. I am also not innocent in this situation, I also said very hurtful things which I feel horrible about, but I always had faith in the love we have for each other.

The details of the arguments and the low points are not really important, but what happened about 1.5 months ago is. We were at probably one of the worst points in our relationship when he sat me down and explained that he firmly believes he is polyamorous and he wants to explore this dynamic with me and his ex-gf. I did not outright reject the idea, and truth be told I was curious about polyamory and exploring a different kind of relationship dynamic. He also made it very clear that I have the choice to not want this and leave. I ended up saying yes and the next day he went over to the ex (now current) gf's house to spend time with her while I was working (this was communicated the day before at the end of our talk so it was all consensual).

I admittedly took it harder than I expected but also not as bad as I originally thought, so aside from a mild anxiety attack, I was okay. It also really helped that I have a friendly relationship with the other girl so it wasn't like he went to a total stranger. He also encouraged me to open up my horizon and meet new people, which after about a month I felt ready for so now I have a few dating apps downloaded which he knows about and is okay with.

But here's the thing. While I'd say about a good 85-90% of the time I feel just fine in this relationship, the other times are very rough. Jealousy, anxiety, fear of abandonment, all those nasty voices in my head, the whole deal most of you are probably very familiar with.

For starters, and this is where the beginning gets important, they have a child together, which in my head automatically makes them a family in my head. He said none of them have the desire to live together (again) and both of them are okay with seeing each other a few times during the week while I am working or when I came back from a night shift and sleep through the day anyways, or where my combined issues render me to bedrotting all day. And i don't mind that, I am truly really happy for him, but sometimes my worries of him realizing he wants to be with her rather than me gets the better of me.

Then there is the feeling of just not being enough. Because "why am i alone not enough?" and "why can't i make him happy?" and the questions that based on my research everyone has gone through at least once in their journey. Most of the times I can deal with those feelings quite well in my opinion, but other times...well. The other times I always end up lashing out and saying hurtful stuff and then I feel even worse, so it's not really helping.

The following list I would also like to go over a few things that made me feel honest to god miserable and i'm not sure where to put them. These are in no particularly in order over the past 2 years and most of them I only found out after he came out as poly and I confronted him:

• He said I am The One for him - I am very clearly not, I am just One Of...
• He said he wanted to marry me - apparently he never wanted marriage, he just said that to keep me by his side and keep our relationship (he literally told me after I asked)
• He said he has no romantic feelings towards his ex - he started loving her at one point again and apparently he thought about it the past like half years, he was just afraid to come forward because he did not want to lose me (again, he told me that almost word by word)

I would also like to admit that I probably have not been acting too nice and once I did throw at him the dreaded question which sounded kind of like: "You are saying you are devoted to me and this relationship and that you love me with your whole heart (which i feel like is just not possible in polyamory), so if I asked you to revert to a monogamous relationship with me, would you do that?"
To nobody's surprise the answer was a very loud and very obvious "no", but I also did realize very quickly that the question was just not right and very toxic from the start and I did apologize for asking something like that.

Still, I feel like I have been lied to the past two years and it hurts, a lot. Especially because if he has been honest with me from the beginning and told me that he might be polyamorous, I would have said "okay, let's give it a try" anyways. I genuienly don't think I am forcing polyamory on myself, but I do think that polyamory was forced on me at the beginning of this dynamic, and I don't know how to deal with this underlying feeling of being betrayed. I love him dearly and the last thing I want is to hurt him, but I feel like every time I speak out about the fact that essentially he lied to me the past two years it hurts him deeply.

And then also there is this thing: Just today I asked him what would happen if he met someone who he feels like is more compatible with him than I am, and wanted that person to live with him instead of me? This was a genuine question from my side, since it affects my future greatly and I want to know if i should have a so called "backup plan". However, all I caused was just a huge argument, him telling me he "does not base his life on what ifs" and that he just wants to enjoy the moment and be present in the relationship. Which is all great and I agree, but also, my brother in Christ, i need to have something definite for my future.

I also did tell him that I do not know what was true from the past two years since lots of things came to surface after, and that i feel like him coming out to me was a huge slap on the face, and my trust did crack a little. But I just ended up hurting him even more.

I know this all sounds like I am miserable in polyamory, but as i said, about 90% of the time I think it works out amazing and I am really excited for him and for me to gain new emotional connections. Or physical, but I am on the asexual spectrum so I want to focus on the emotional aspects.

I really, really want to be able to enjoy polyamory to the fullest but I am also really, really tired of hurting my significant other who most of the time seems to be honest with me. After all I do love him even if he put me through a great emotional turmoil. I am also very scared of being hurt again, of my trust being played again.

All in all, I am not sure how to deal with the evil little voices in a way that is healthy for the both of us, so I would really appreciate if you guys could share your tips or practices that have worked for you at the beginning. I am aware that not all of them will work for ME specifically and that this relationship might not work in the future, but right at this moment I still have a positive outlook on it.

Thanks for reading or i'm sorry for wasting your time, i hope y'all have a great day x