My backstabbing fake friend

I told my friend, let's call her Sara. Sara and I had started talking to recently. She was a sweet girl and I trusted her a lot. One day, I got sat next to this one guy in class. I thought he was nice and we talked a lot and I started to like him. I thought I would be no harm in telling Sara about my crush. After all, I trusted her. What could go wrong?

The guys, let's call him Jim. Jim and Sara had had never talked to him, much less even look at him. But immediately she started talking to him. I didn't really see the harm in that at first. But thinking back on that, I really regret not seeing it faster. Sara also does valorant with Jim so they call often. And one day, Jim said he liked someone to Sara. He didn't say who but he described her. As my friend described her, I slowly came to realize that Jim was describing Sara. I felt disappointed rather than jealous.

I contemplated whether to tell Sara that he liked her because she seemed to not know. However, if my friend liked my other friend, I wouldn't stop them. So I told her. No reaction whatsoever. If my friend had told me that I would have said "Oh I'm so sorry. I won't ever like him" or something like that but she just said yeah. What kind of reaction was that?! Not only did she break the first rule of girl code and chase after my crush, she doesn't even care about what she did. This isn't the first time. My other friend also told me that once she told Sara about her crush, Sara immediately started talking to him. And as I was figuring everything out, my friend told me that Sara liked this other guy. Now, only did she just come after my crush, she came after my crush while liking someone else! Like please stick to one guy.

I really don't want to talk to her but she always has lunch with me so I have to see her. And Jim isn't the best guy either. It is clear as day that he is into her now. He and Sarah talk to each other while leaving me to this wheel on the side. Like hello? Atleast include me in. And Jim ignores me. And I swear to God that Sarah told him that I liked him. I dwell like he's ignoring me and avoiding me because of that. But that isn't an excuse to be disrespectful like that to me. I thought we were friends. No need to be rude. Both of them are trash and I'm trying my best to ignore both of thembut Sarah is a mutual to a lot of the people in my friend group. Sarah is an honest pick me. She makes her voice higher around guys and she laughs like she's flirting with every guy. I'm so tired of her. I'll make sure that she gets what she deserves. If you wanna act petty, I'll act even more petty.

What should I do?