it is in the notes, just hover on the boys picture and the bottom right will show a hear meter. For dialogue options it most likely due to ur stats instead of ur affection level with the boys. Kindness usually have to be 50 above to open options

Oh you can find the clues in various places, like for the first password to open the diary, its from talking to an npc near a bench in the shops, for the first diary entry, it's from meyza's nickname to you during your conversation, the second diary entry is mentioned by the MC multiple times in Io's arc and in the potion classroom, third is when MC meets the principal the first time, in the guide, I just state the passwords as is since basically the answers are all already stated as you play

Did u crush the flower? Ur other stuff also might effect his heart level tbh as just because you didn’t interact with him directly some day to day choices may affect the boys opinion on u

But def for a fact if u crush the flower, especially if you trip him, he will hate you and its hard to form a connection with him unless you make him ease up to you after visiting Leynar before the jellyfish festival