I do think that Yuu already had an idea that Kou and Ginga had sec ... When the doctor explained the thing about them reacting to Yuu's pheromones, the look that Yuu gave them made me realize that yeah, so he somewhat knows that they've fcked but he didn't pry abt it (well it's just my interpretation tho) Also, it seems like he won't actually hate the two of them if he knew that they were fcking before.. I mean he already saw the two of them kiss while the three of them r doing it so no doubt..He loves the two of them so I guess he's ready to accept them..
I do think that Yuu already had an idea that Kou and Ginga had sec ... When the doctor explained the thing about them reacting to Yuu's pheromones, the look that Yuu gave them made me realize that yeah, so he somewhat knows that they've fcked but he didn't pry abt it (well it's just my interpretation tho) Also, it seems like he won't actually hate the two of them if he knew that they were fcking before.. I mean he already saw the two of them kiss while the three of them r doing it so no doubt..He loves the two of them so I guess he's ready to accept them..