You seem to want to read things so here are some links to "hub" type pages to start. YMMV.
Sometimes people agree to polyship and go in from a foundation of respect knowing that they are taking risk. They risk trying something on that might not fit them... or it might fit them... but not the other people. And because those are not "it fits everyone" so the thing can continue then they may break up all the way down to "everyone single" when the polyship disbands.
You entered into something that you did not want for yourself. It does not sound like it is coming from a respectful foundation. You have already tried it once and came to reaffirm your original belief -- it is not for you.
Learning about poly is fine, but if you already know
it is not for you with these people and your heart is not in this... learning about poly to avoid having to move on to the next order of business is wasted energy and emotion. Your energy could be better spent dealing with the next thing now instead of later.
You are very clear about your expectations in your first post.
We made the agreement that we would try it for a month and if I found at the end that I couldn't do it, we would dissolve the relationship and our relationships would go back to the way they were.
I have greyed out the back end. It cannot "go back how it was." You are all changed for having had the experience. But the rest is very doable and reasonable. You all could stick to your shared agreement and dissolve the polyship.
You don't have to feel wonderful about it while doing it. But you could do it, and then you could deal with the next question.
If you meant "go back how it was" like -- (You + bf) and (friend) on her own? Could ask him if he is willing to do that.
To me? He does not seem to plan to honor it, since he is pushing for you to continue in polyship. I think you basically have your answer. Just not acknowledged by any of you. But I could be wrong. I'm not in this.
Just to be clear and confirm it for yourself you could state to BF:
"BF, I made this agreement. I tried for a month. Did not like it. Conclusion? Polyship over. We are all single now. Done. Old business concluded now that I have made you aware. I kept my side of the agreement.
New business. I would still like to date you BF in a monoship shape. We would have to start all over. BF, you up for that or not?"
Then accept his answer. Yes or no. If there is hemming/hawing? A less than forthright "no" is not a "joyous yes." You deserve to be with someone who is thrilled to be with you. Not lukewarm
to be with you.
I would strongly suggest you just move on and NOT ask him to start a new monoship with you because he wasn't very respectful in this whole journey. His character seems weak. But "Does this man make a good BF for me?" is a separate question than " Do I want to conclude old polyshipping business or keep it hanging around just cluttering my life?"
I suggest you conclude old business and get it off your desk. You tried. Did not like it. Polyship is over. The only thing left is to tell the people involved that you are done and BE done with polyshipping with them.
You are very clear in what you DO want also.
I was much happier when it was just me and my boyfriend and that was it.
Could actively seek your happiness.
Could stop putting your energy in the (learn about polyshipping even though I don't want to polyship) bucket.
Could put your energy in the (I was happy monoshipping with BF) bucket instead and move that forward.
You could ASK him if he is willing to be the BF in a monoship with just you. Get on with the show. And deal with digesting his response whatever it is.
You can do this. Could be brave, and could attend to your unfinished business. Could be brave and go for what YOU want. You CAN handle living your life and dealing with the things that happen in it.