Would it be best to go to the party or just be 'busy'?

My best friends and I have gone to different highschools, and we’ve become different people.
When we were all in the same middle school, I was the butt of the joke, laughed at, but it was done so “affectionately”. Now going to this new school without them bringing me down all the time, I’ve felt like a better person, and I’ve been treated very differently.

While I still generally like my old friends, I always feel ugly, awkward, and stupid whenever I hang out with them. I’ve realized that hanging out with them has become me trying to impress them, make them see I can also be pretty, funny, and everything.

I hung out with them a final time and it was a big, happy sleepover. Except I ended up feeling depressed by the middle of it. I felt like they were secretly exchanging looks, and it might’ve been me being paranoid, but I couldn’t shake the feeling and I went home early.

One of their sweet 16 parties is coming up in about two months, should I start distancing myself so it’s not a surprise that I don’t go? Or do I suck it up for old time’s sake and convince my mother (Who definitely isn’t a fan of this crowd) to let me go?
(Again, I still like them for the most part, they are all very very beautiful and interesting people, they just have become more shallow and I don’t feel good around them anymore.)