The first part of the dream was at a party in an unfamiliar house. I knew a few people but the rest were strangers. I wasn't seen until the end of it, I went into this room to find one of my friends from my old school. She usually is very cautious and wouldn't really try anything daring. I walked in on her smoking pot. she asked me "Hey Jess, wanna try it? Just once" I said nothing and walked out the room and found myself in a gym class that I had never been in. I sat down in the group of students like I would any other day. I saw this really attractive guy sitting next to me, listening to the teacher talk. Suddenly the guy turn to me and said "We're gonna be dancing soon, I hope you don't have a partner already." One of his friends said something that I don't remember and before I knew it, the attractive guy's arm was around me, like we knew each other. I believe it was my first day at a new school (in the dream) but in real life I recently finished off the year at a new school. He just kept staring like he was in love with me, but I felt it too.

and then i woke up, very confused and sad
This dream barely make sense but I think it means something

In the dream, your friend who is normally cautious, wants to try something new (smoke pot). This could be a message from your unconscious that you need to be brave about something.

A dream about dancing with a stranger can be a sign that you want to start a relationship or you want a relationship you are already in to go further, so the attractive guy asking you to dance can mean that either 1) you're looking to meet someone new if you aren't with anyone already or 2) if you're already with someone, you want that relationship to go further.

The dream could be telling you that if you want to make it happen, you have to be brave and take matters into your own hands.

It's interesting that you felt sad when you woke up, even though it was a good dream. Did you feel disappointed that you don't have someone like that in real life. That could also be a sign that you need to make a change.