I've been dating my GF for about a year now. It's always been sort of an open relationship but up till now I've made it super clear that I'm looking to date other people. She was ok with an open relationship because she thought I only wanted no strings attached sex with other girls. I want to date girls and potentially get to know them. She isn't handling it well. What can I do to salvage this?

More of a theoretical question: is it possible to be in happy long term polyamorius relationships? Has anyone had experience with such matters?

Sorry for any mistakes. I'm on my phone.

_________________
Note to self: Don't Trip

You could try and be honest with her and tell her to avoid drama. If she agrees then all good.
On the other hand you could just tell her the (BS) story that love is something that you can give to more than one person.
It is like having two kids. You love them both equally.
And if she says that is not right you can tell her that she is acting like a selfish only child that doesn't want a little sister.
And that's how you feel. You want to expand your love to keep it new and exciting.
You can find some internet "evidence" on testosterone and hormones and how this could keep you even happier and closer to her..

I personally don't understand women that can work on poly relationships but from what I've read on forums and comments on articles the ones who were accepting it had a similar explanation to what I told you. In fact that was one of the women's stories. They were happy.
Some of them had low sex drive and were even happier to let their partner have another gf.

If she is "spiritual" you can also use quotes from the Bible or Quran or any other Holy Book.
You can talk about kings that had lots of wives.. or Abraham that had lots of women or other prophets etc
Other examples you could use is how people used to live in tribes and the love that had someone for each one of their wives. You can also tell her the (BS) that this is more in human nature etc.