What are people coming to?

I haven't slept much last night. Stayed up until 4 am talking to Polly about things we once discussed on a daily basis, but not anymore...
Yesterday I realized that I'm not completely over Michael (long story short, we were going to go out but he decided to mess around with Lina, the cheap and easy slut who tried to fuck every guy in the school) right after my birthday. Out of curiosity I decided to ask my loyal friend Amanda what really happened when she and Finbar saw them, and she told me there were clothes taken off... Michael and Lina were going to have sex in our GEOMETRY room. In SCHOOL of all places. What my friends did is they kicked tin cans until they saw them, and when they did they were really - and I mean REALLY - embarrassed.
When she told me this yesterday, I started laughing. It wasn't one of those laughs that would make me cry later on, but more of a "How fucking desperate can you get?" laugh. Whenever I see him, I just think of how sad he really is.
Now, the thing is, he's doing all of this to my friend Sara what he did to me: get really close, then after a while become really fucking distant before messing around with another girl. I want to warn her about it because he did the same thing to my friend Orisha before he did it to me, and she warned me about it months before. Should I do the same? I know he's going to end up screwing her over for a fact, and even though I'm not exactly over him I don't want to see her get hurt like I did. Should I warn her or just let him do his thing?

On another note, I realized that the new kids here are a bunch of immature brats who think going to parties and shows and getting fucked up is the new cool thing to do. This one girl - who intimidated me at first - named Molly, is a perfect example. Yesterday, when Amanda and I were talking about serious stuff, she asked us if we had any plans, and we said no. She did manage to tell us this:
"Oh. We're going out to parties and shows."
She thought we were actually JEALOUS of her when it was the opposite. I told her to have fun getting fucked up and then turned back to Amanda before moving on. Why would you tell anyone that to make them jealous? It just makes you like some spoiled brat who has nothing better to do than talk about doing ecstasy when half of the time they more than likely haven't, since they actually brag about it... And that is exactly what she is. An immature brat.
For the record, she's only fourteen... which makes it even worse.