Friend problems

So I kinda have this dilemma about a few friends of mine. Let's call these friends 1, 2 and 3. Friend 1 and I have been really close since we were in elementary school and now being in University, we're not anymore. We stopped talking although I have tried talking to her over Facebook a couple of times. Ever since her birthday party in November (going out to a bar, which I couldn't attend due to school work) she and friend 2 and 3 went out with a few other people. All 3 are always hanging out together and I just seem to be left behind all the time. I always see Snapchat stories of them hanging out. They haven't made any effort to actually talk to me since her birthday and I'm pretty bummed about it. Am I overreacting? What should I do?! Help!