Every time I do a new run of BaDIK, you find new things. Lily openly talks to Mona here. Through Mona, not only does Lily know about the prostitution, but Stephen does too. Quinn could turn the tide with Mona through intimidation.
Is Maya the other Mona? In EP9, Maya and the MC will probably meet Stephen and Jade. Stephen was already curious and wanted to know from Chad why he attacked the MC. Maya already told Sage in EP7 so Quinn offered her the tuition. Thereupon Sage was pissed off, but dismissed it with that for now so Quinn would have a special sense of humor.
I imagine the scenario of the conversation like this. Sage, Maya and Stephen are talking in his office. Meanwhile, the MC goes to the bathroom because he just found out so Sage is a Burke. Either he fucked Sage and/or Jade or he didn't. It doesn't really matter because Tybalt exists. The MC was at Villa during the preps party. Sure Sage saw him, but there was also the sprinkler incident that Tybalt blames the MC for. There are enough reasons why the MC is in the bathroom.
But the reason Sage is mad at the MC comes from the conversation in Stephen's office. Stephen will ask Maya about the rumor, he wants to find out the background, just like why he asked Chad about why he attacked the MC. Maya tells her story much like she told it at the end of EP6 to Josy and the MC. She mentions so Quinn offered her and Mona the tuition. Because of the incident with Mona during the preps party, he connects the dots. Mona is offering her sexual services and has been offered the same tuition as Maya. In doing so, Maya is also likely to say so she knows from the MC what Quinn is doing with the girls. Sage hears this and of course is upset with the MC for not telling her.
The MC will be under a false assumption as to why Sage is so pissed off at the bathroom door. He figures, probably so Sage just found out so he was involved in the sprinkler incident.