I am looking for the title of an old yaoi manga it's not a webtoon from what I remember there are two siblings the younger one becomes friends with the master's son. They become good friends until he finds his older brother sleeping with the master he gets upset about it and finds out his friend knew the whole time. He tries to leave but his friend doesn't let him and forces him to stay with him that's all I remember

This sounds a lot like "Saihate no Kimi e" by Minami Haruka
link: https://www.mangaupdates.com/series.html?id=1033