I'm upset that my boyfriend is about to get an amazing job in another state
What about his new job upsets you the most?
If he leaves I'll need to adjust to another city
It can be scary when facing a big change like this, but it is also an opportunity to find a new and better job for yourself! This could be an exciting chance to advance your own career and support your boyfriend.
I don't want to move because I want to keep my old friends.
I understand that completely, I'd miss my old friends too. But maybe you can get a new job yourself there too and meet new people. Your fears are getting the best of you, just go with it and  stay positive.