Thanks for writing your first post and sharing your thoughts.
i am much o,der than you and I find friendships tricky st times. Sometimes when someone has. Girlfriend or biyfriend they have less time for their other friends even if they don’t intend to. A boyfriend may want your friend to spend more time with her. She maybe is getting to know her boyfriend and so things will change.
I can understand how puzzling your friends behaviour is to you.
I think if you wait she may change. Can you keep in touch via text or even write her a letter.
All problems need understanding. Thanks for sharing.