I have been looking. For this manga for a while and I have looked everywhere but can't find it. It is about two high school students. One is from a rich family and is currently living with his aunt and uncle. I think the uncle is a politician or at least someone of great importance. The uncle often looks down on him and ridicules him for not being as perfect as his cousin. It is also later revealed that he had some feelings toward his cousin at one point. The other character starts a relationship with their her protagonist. He might have walked in on him with another studnet I am not sure. Also, he goes over to his house near the end of the story and gas intercourse with him. He meets the cousin and the cousin tells him to keep it down so that the aunt and uncle will not hear. the two ingots him and have intercourse in the bathroom and that is when the cousin confronts them. At the end of the story they have a relationship.

Are these posts also seeking the same manga?

http://www.mangaupdates.com/showtopic.php?tid=53688
http://www.mangaupdates.com/showtopic.php?tid=53701
http://www.mangaupdates.com/showtopic.php?tid=53710
http://www.mangaupdates.com/showtopic.php?tid=53724

If so, then you therein mention a few other details that might prove helpful to someone (else) who's able to identify the described title.

Sorry. Good luck.

Is it Slave x Slave?
(It took me a while to find it since I didn't like it and wiped it out from my memory)
There are a bit of differences tho...like he's the half brother and not the cousin and the promiscuous guy was with a teacher and not a student (when he got caught in the act lol) but what ever, the rest is exactly the same.
I'd also like to add that instead of making multiple posts about the same question, why not add all the details in one question and bump it after one week.
🙂