People grow and find mew paths in life, but that doesn’t make the prior less significant. I imagine your friend got used to spending so much time together and now feels like the friendship is in jeopardy, or maybe she genuinely misses all that time with you and feels more possessive because she wants to spend time together.
But I feel like all the time with one friend can take away a sense of individuality and restrict perception a bit. Being exposed to the familiar isn’t bad, but seeing and learning new things can lead to experiences you might miss out on.
Maybe it isn’t too bad if you have genuine common interest and you have plenty to explore together. But you shouldn’t feel guilt for hanging out with the new student because they bring something wonderful to your life.
Me and my best friend from highschool had maybe 2 or 3 years that we barely talked. With me being in a relationship and working and him going to school we didn’t get a whole lot of time together. We still were able to look back at how much we grew together and enjoyed our time, and at times we might meet up to hang out and catch up over a meal, but not as often as we once did.
And now we hang out on discord everyday, with a few other friends. Maybe not like before, but it is still nice to hear from him. And w e have a fair amount to talk about from time to time because of some of the stuff that happens in our personal lives, certainly more than we knew.
I say the important thing to mention to her that you still value her as a friend and that you still think of her. You might have your time divided between two people but you have a heart big enough for both.