The most important thing as a takeaway here is actually: "I don't remember everything."
You were in a triple makeout with hot girls, and you don't remember everything. For the REST of your life, you are going to know that you had that experience, and because you were too loaded to process it, you don't remember it.
What if you don't remember the BEST parts? How do you know you didn't have a threesome, if you don't remember?
Don't explain to me all the reasons why not. I realize it's not likely. The point is that you don't remember, and you probably weren't in control. (Your game, however, does appear to have been on point.)
So stop getting so fucked up that you are blackout drunk. If there's one thing worse than waking up and finding out you are in jail or have knocked some girl up, it's being so drunk you don't even remember doing the think you're being punished for.
Thus endth the lecture.
Now - to your point. Here's what happened: "I had a bit of a thing with Liz we hadn't escalated yet."
You're probably right. There was chemistry here with Liz. But you haven't opened yet."
Now: "I tried to initiate with Liz but she wasn't really into anything when I noticed Sarah giving me serious IOIs"
If you noticed Sarah at ALL, it means you hadn't isolated Liz. You're trying to make out in the same room with other people? Yeah, I did that when I was a teenager, too. But it's probably why you weren't making any progress with Liz. This is anti-slut defense. She doesn't want to be perceived as a slut by other people, so she gave you the stuff arm, even though she was into you.
How do I know this? Because she jumped in with Sarah. Many straight girls will do the girl-girl makeout thing to draw male attention. She was trying to draw your attention away from Sarah, who was, if not DTF, certainly down for makeouts.
And it's common to have drunkard's remorse when sobering up. Yeah, she feels like a slut. That's because she acted like one.
What you do next depends on what you want? The bang? LTR? Just friends? FWB? Or just to make her feel better.