After you got kicked out of the Bathroom at night by Satsuki you need to talk to Fumiko in the kitchen at afternoon ... satsuki will apear and talk to the both of you about that Bathroom incedent.
Now wait untill next morning .. go to the Bathroom where Fumiko is ... then leave and she will stop you .. wich leads to ... well i guess you know ... after that its actually only talking with the two of them in diffrent rooms