I have a question. When Yosuke no longer appears in the park, is it because I'm ready to take Key's room key and open a door that appears when you run really too much 
, or is it because Did I do something wrong and now I'll never be able to open that door again? Does that mean I won't be able to open that door at all?
"Do yosuke's quest
- attend Friday party
- meet Yosuke at night day after party
- get the thing for him from science student (random event during the day)
- attend 2nd party
- meet up with yosuke again to give him the thing, he will ask for pizza
- cook pizza in the kitchen
- meet up with yosuke, he will point you to kan's room
- attend party to break into Kan's room to get lab key
- run until you reach lab"