My first therapist was through the counseling center at my university, so I know what you are experiencing. They are not generally allowed to continue services to students who are not enrolled in the university.

He is the one I've kept in touch with since I graduated in 1985. We don't have frequent contact, but we do keep track of each other and keep each other updated about our lives. He's retired now, so we don't have quite as much contact. One reason it worked was that we simply kept in touch for professional and social reasons. By professional, I mean he was the director of career services at the university, so initially, that is why we were in contact. He was assisting me in finding my first teaching position and in deciding/finding a counselor where I ended up. After that, we just kind of kept in touch several times a year and that has kept on up to the present. One reason that kind of contact was workable was that I didn't contact him really as my therapist anymore; that aspect of our relationship was over. I didn't have expectations of anything at all really, so it was a pleasant series of events that led to a lasting friendship.