i believe you have to trigger his route first by approaching him in study of malediction (which is the only class you'll ever have with him) so afterwards you'll have to initiate events with him either by having lunch with him, skipping class, or during free time. some places he frequents are: library, garden, forest, and kitchen. hope this helps :)
if you can’t find him during lunch, then try looking for him during free time or when you skip class in the locations specified. there’s a very good chance you’ll find him eventually while skipping class as you only have 1 class with him, so i recommend building up on BAD and skipping frequently. that’s how i initiated most of his events after my second interaction with him.
as for how i got the second interaction, it might’ve been luck, but i literally just chose his icon when it was time for lunch and it initiated it for me. when i did, it took me to the garden, so maybe try going there more often?
if you’re still having a hard time finding him after doing his first interaction in s.o.m then it might just be the rng messing with you atp :’) or your game is bugged, this has been happening to a lot of people tho so if in doubt, just reinstall