If someone suddenly disappears from your life, on a good note, you do remember that friend from time to time. Provided the disappearance was on a good note and very sudden.
I have had a student, a good friend simply disappear. I sometimes wonder if it was because of something I said or perhaps I was too old to be his friend... I sure as hell wish it wasn't because of something bad happening to him... but whatever be the case he disappeared while our friendship was still nice and now from time to time I do remember and pray for him.
I have taught a lot of people, but made only one friend among them... so it's a little sad to have him disappear but that's life I guess. People stay if they want to, and don't if they don't.
One thing is for sure though, as teachers, we really care for each of our students. I never knew why some of my teachers were so nice to me... but now I know. it comes from within, you just really want to give your best and help your students grow.