How long is your programme, three years or four?
Colleges, conservatories, universities always have a rapid turnover of a student body; this is inevitable.
However, that is no reason not to see your graduating friends again, and, moreover, modern means of communication (including social media platforms) will allow you to keep in touch with them in a way that was not possible with earlier generations.
More to the point, even when - and if - you do meet some of them again, - despite the shared past, the shared interest in music, and the shared world of working professionally in music - things will have changed; they will have changed - personally and professionally - for, the world of work is different to that of student life, and, in addition, as time goes on, some of them will find life partners who will have become, perhaps, a more pressing priority in their personal lives.
In any case, when you return to college, I daresay that you will find yourself among the seniors - and therefore, you may find yourself mentoring, teaching, guiding, advising - people studying music who are junior to you, some of whom - as is inevitable - will also become good friends.
And, given the very intense environment of a college education, where your entire day (environment, life, world) is taken up with shared activities, such as the study of what you like in the company of many others who also find this shared subject matter of study to be of compelling interest, I would be very surprised if you did not make fresh friends over the coming terms and years.
Anyway, my counsel would be to be open to the possibility of new friendships, and to be prepared to put the time into sustaining and maintaining your existing friendships, even if they have graduated.