Even though we haven't met yet, they share some common friends, none of whom I like. Can I tolerate them for 30 minutes to an hour? Barely... Could I tolerate being near them if I knew they had a romantic interest? Absolutely not. Her friends have a "I know more about anything you have studied about" attitude and are generally abrasive to anyone who doesn't acknowledge how smart they are. I may be projecting some of my feelings from them onto him, but I really don't trust myself to be in the same room as him.
You don't have to be in the same room as him. If she's pushing you to meet and hang out with this guy, tell her firmly no. This is called parallel polyamory, where the two metamours both date the same person, but do not meet. This is ideal for some people.
If you yourself feel you need more friends, fine. They don't need to be her "know it all" friends. You can get your own.
I have read through many of the resources you have posted. I think it's her NRE that's got me feeling this way. Her not being around to talk to has made it worse, though. My main reason for posting here is to talk with people and see if by chatting I can isolate these feelings and work through them.
She hasn't been around to talk to much? Why not? Is she neglecting you now in favor of her friends and new bf?
I am glad you reached out here.
I am still confused as to why you said you and long-term-gf started out non-mono, but the practice of polyamory seems like uncharted territory to you still. Could you explain more?
I have been talking through this stuff with her when I can. I'm horrible with starting difficult conversations. If you know how to find out what triggers feelings, that would be great, because I have no clue what my triggers are. The feelings just come and go, or they stay and I stew in them for days or weeks at a time. I also tend to withdraw and try to hide my emotions, because I hate drama, but then that just starts drama... The cycle continues.
Avoiding "drama" downplays the validity of your feelings. I know. Men in our culture aren't supposed to have feelings.

They are meant to push them down, and just be brave, stiff-upper-lip warriors. It might be partly hormonal too, imo. I am assigned female at birth, but I ID as non-binary. Menopause made me even more like a guy, with the drop in estrogen. I find myself rarely crying, even when a good cry would help, a lot!
Sometimes I have to find a way to MAKE myself cry, for my own good. Then my emotions flow more freely. I might cry a little more, too, for a week or two. That seems to hoist me up to a better place, get me to a new stage in my life. The flow of tears clarifies, and even washes away some of the pain.
Go ahead and cry now, buddy. We don't mind.
But, I do know and understand my emotions, and other's emotions. I've been deeply trained in this, through motherhood and my former career as a lactation consultant. Identifying emotions and handling them in a healthy way could not be more important. And if you want to be successful at polyamory, you simply must learn to be better at knowing yourself, understanding your partner(s), and communicating in respectful, helpful, open and honest ways.
I used to not be so emotional... Then I met my GF who I had a poly relationship with... Now, when she gets home, and we have a more in-depth talk, I'm scared I'll wind up in tears.
And you don't want to cry... You're trained to be stoic, like a Spartan warrior, or like an early human, hunting in the forest for game, with a spear, and not able to stop running because a branch stabbed you, or a bee stung you. That behavior is all well and good in war or hunting, but not so helpful in romantic relationships, especially polyamorous ones.
I have seen that most polyamorous people prefer others who are open with their emotions, and savvy about how they express them. Non-Violent Communication (google it) works well.