I have friends, but still feel "lonely" at times?

So, when I usually make new friends every year, I’ve noticed that some of them are already in groups that would always hang out with each other. Now, this made me feel like an “outsider looking in” because even when I see them out and about, they still wave or talk to me, which is still good. The problem started when they didn’t invite me to eat or go to parties with them, but they still were happy when I would “meet up” with them at parties or the dining hall. Now, I understand that I may be viewed as an acquaintance to them, but it still confuses me why they never took the initiative to invite me? Should I start to ask them instead? They already seem to enjoy my presence, so why not?

Even though I’m currently apart of several friend groups at college, I still have some of my closer friends as well, but my extrovert personality makes things interesting. So, I’ve made some questions on how to deal with this:

  1. Should I ask to hang out with my acquaintance groups more often?
  2. Should focus more on my close friends instead?
  3. Did I explain this thread thoroughly enough?

Now, I’ve recently began hanging out at my friend’s off campus apartment every weekend before the parties took place that evening, (pre-gaming), which gave me another thing to do on Friday or Saturday night instead of playing video games or browsing on my laptop.