What I did was that I chose Bellatrix and I made sure I had crypto, astrology, combat and defense, and you can choose any other class you want. Before Tuesday make sure you get your bad up to 4 and strength up to 10 or you won't be able to ask about his smile. On Monday attend your classes but during freetime I chose to steal food from the kitchen TWICE which then you would have your bad up to 2. Switch to the battlefield to excerise and around the end of the day go to the battlefield to choose "be a delinquent". On tuesday when it asks you to go to class say no and skip. During your skipping period go to the forest or garden to find bugbear (I preferably went to the forest). There's a chance you'll find somebody different instead of bugbear but thats okay cause you can still retry and get bugbear! When bugbear asks if you "want to have fun?" say yes and so on. Make sure to go to the battefield and build up your strength up to 10! The next day try to spend more time with bugbear (there should be an option to choose bugbears icon during freetime/extracurriclers). DONT SKIP your classes cause he will be in one of them which then you will be able to ask questions! Make sure you ask about his SMILE to get the good ending! Bugbear will say something about the library but you dont have to go there yet, try going to the library on thursday or friday (from what i heard). I specifically went to the library on friday 8:00 pm because it showed me a different person in the library on thursday. DONT SKIP your classes on thursday or friday because for me I got the crypto class on friday which you need to ATTEND that class in order to learn more about "bugbears" which will lead you to bugbears route!
That's mostly it! I hope it helped and goodluck! If you still have some trouble i can try to help!