It's amazing how people come out of the woodwork when you put yourself first & say "yeah, I get that you suddenly don't have anyone to go with you to X but I'm doing my own thing," or are just generally having fun being you. Because you're an amazing person and they're fucking up and missing out.

As someone who felt this way for a super long time, the solution isn't fun in the beginning, but it is worthwhile. Get comfortable being alone. It's hard, but you need to change your mindset from you being unwanted/a backup, to others not prioritizing you like they should.