second couple syndrome strikes yet again..

The ML is the Prince's (or he has already become the King) younger brother. The MC was married off to the Prince's younger sister. The sister d!ed even before all the rituals could be completed and therefore they did not consume the marriage. But according to the law, whoever gets married into the royal family can't remarry or take a s*x partner even if they become a widower/widow. We readers can see that people gathering at the Princess' funereal way pitying the Groom cause he's so young and would have to lead the rest of his life without a partner. The Second prince arrives at his sister's funereal and we can see MC getting flashbacks of getting sexually assaulted by this prince. It happened right around the time he was getting married to the Princess (the night before or after, I'm not sure). We gradually find out that the the Crown Prince is also weirdly obsessed with this royal groom. They all grew up together by the way.