Thanks, MickeyCheeky.
I will try my best when I get back to my university some time next week (I travelled home a few days ago to visit my family, since I currently have a short break between study periods).

My current "plan of attack" is to actually show up somewhere where some of my former classmates will be waiting for a lecture to begin (I can find their schedules quite easily on our student page), and start a quick conversation with them there.
I know that some of them liked me in the beginning since they approached me with a smile and started conversations several times before they became insecure around me, and it has always annoyed me a lot that they have got that impression of me.
It would mean a lot to me if I could start conversations with them at some point and show them a bit of my real self.
I feel like this might be a good first step.