conflicted to stay or leave my friendship group

Start with this mantra: "Their conflicts aren't my conflicts."

Now say it to both sides: "Your conflicts aren't my conflicts. I can love both sides. And while I don't expect you to love everyone, I do expect you to respect my rights and feelings in this matter. If battle lines are being drawn, then I am neutral Switzerland."

And mean it. Stay out of the conflicts. Change the subject when one of them wants to trash another one in front of you, even if there are others around. Just say, "___ is a friend of mine. Please don't trash them."

You have the absolute right to get up and leave (or hang up, or log out, as appropriate) if someone disregards your feelings in this manner.

Largish friend groups tend to break down over time. It's not necessarily due to conflict. It can also be that you start to be at different stages of your life. If someone has a kid, they won't be available as much. If someone gets married or is otherwise in a super-serious relationship, they might try to bring their SO along, and that changes the dynamic. Another person might move away. Yet another might get a high-powered job where they end up having very little time for socializing.

All of this is fine and normal and, frankly, should be expected.

Recognize, too, that these aren't the only people in the world who you can ever be friends with. There are a lot more fish in the friendship sea, and you can dangle out your hook and bait it with things like being friendly to your neighbors, joining a Meetup group, volunteering, going to a gym, or doing any of a thousand things you can do to meet other people. You're not being untrue to them if you hang out with other folks. You're expanding your friendship circle. And there is a lot that is right and good about that.

Oh, and one more thing. You've had a great two years with a terrific group of people. You've been able to open up, relax, let your guard down, and be yourself.

That means you can do it, and you can do it again.